Since the beginning of this year, splashes of yellow, orange and silver have been perking up Singapore's public spaces.

Brightly coloured bicycles from three firms - oBike, ofo and Mobike - can now be found at MRT stations, parks and the void decks of Housing Board flats islandwide.

There were mixed reactions from Singaporeans who spoke to The Sunday Times about bike-sharing schemes, with some finding them easy to use, with others having trouble finding the bikes. Some use them for fun, others for work.

Economists also weighed in on the big picture, with some observers wondering if the firms will be viable in the long term.

Students have found it convenient, said a spokesman for Singapore Management University (SMU), which has more than 100 students signed up with Mobike. It tied up with the firm to place 20 bicycles at its campus and hostel.

"Informally, students have given feedback that the service makes travelling between the hostel and SMU campus convenient, and useful for exploring different lunch spots," he said.

At least two other users ride the commercial two-wheelers for work. Social worker Omairah Amrhan, 23, said she had been using shared bikes for about two weeks to meet clients at their homes. She likes the convenience of being able to park anywhere.

While the bicycles cost between 50 cents and a dollar per trip, regular promotions mean they are often available for much less or even free.

Food delivery man Mifzal Shah, 20, has been enjoying ofo bicycles' free promotions, saying: "I find it's useful for me since I don't own a bicycle."

Accountant Steve Wong, 40, who tried an oBike for the first time on Thursday evening, said it was not suitable for him since he cycles between his home in Punggol and his office in Changi every day.

"It's easy to use and the price is reasonable, but the bicycle is too heavy," said Mr Wong.

Some users found the GPS employed by the apps unreliable. "Sometimes the bikes are not where the app says they are," said Ms Omairah.

On Thursday, ST experienced the problem with both apps that have GPS. The oBike app showed a cluster of about 10 bikes at a block of Ang Mo Kio flats but none was found at the void deck. It is not known if users had taken the bikes up to their flats.

At Punggol, ST found that a Mobike bicycle parked next to a cycling path was invisible to the app.

Mobike international expansion head Florian Bohnert had told The New Paper previously that buildings and "other possible obstructions" could affect the accuracy of the app's GPS.

ofo's app does not use a GPS.

While there is no hard data on bike-sharing usage, the number of bikes has been steadily rising.

ofo said it has about 1,000 bikes in Singapore, but the other two companies declined to give figures.

The authorities said the companies have plans to introduce "many thousands" of the two-wheelers over the next two years.

The share-bikes are now so ubiquitous that the Government announced on Friday that it is shelving its own plans for a national bike-sharing scheme, which was due to have launched later this year.

Economist Walter Theseira said the decision made sense, given that public bike-sharing schemes, which usually come with docking systems, required substantial funding from sponsors and governments.

Despite sponsorship from advertising company JCDecaux, Velib in Paris, for example, is said to cost the city about $22.7 million annually. In contrast, private bike-sharing start-ups receive considerable funding from investors.

Dr Theseira said: "Private capital is pouring into these firms."

ofo - named because the word is shaped like a bicycle - is backed by Chinese ride-hailing giant Didi, and said to be valued at $700 million.

Mobike - which has more than one million bicycles in China alone - announced last month that it had raised more than $425 million in funding this year, with Temasek Holdings and hedge fund Hillhouse Capital among the investors.

oBike did not respond to queries about its investors.

The three companies in operation use mobile apps that locate, unlock and pay for their brightly coloured bikes, without any docking stations.

Dubbed "Uber for bikes", dockless bikes first emerged in China just two years ago with the founding of Mobike and ofo.

Mr Francis Chu, co-founder of cycling group Love Cycling SG, estimates that under a conventional, docked bike-share scheme, the budget for a high-tech bicycle and two docking points would be more than $4,200.

In contrast, an ofo bicycle - not needing any docks - costs only about $60, said Mr Chu.

However, it is still not known how viable these firms will be in the long term, say observers.

"They are probably operating at a loss, spending money to grab market share," according to transport researcher Alexander Erath of the Future Cities Laboratory.

Another area of concern is the lack of regulations, for example, over parking. In both China and Singapore, there have been complaints about indiscriminate parking.

ST found 40 shared bikes parked illegally in motorcycle parking spaces at Pasir Ris Park last month.

Dr Theseira said additional parking areas at places such as MRT stations may be a necessity.

"One possibility for regulation is that these firms pay taxes to bear the additional cost of such infrastructure," he said.

National University of Singapore transport researcher Lee Der Horng believes that a regulatory framework will eventually be introduced, just as it had for the previously unregulated private-hire car industry.

The Land Transport Authority (LTA) has ongoing plans to expand bike parking facilities for all cyclists, and said "strict enforcement action" will be taken against indiscriminately parked bikes.

"This includes impounding of the bicycles and heavy fines, including against dockless bicycle-sharing system operators, and if necessary, regulatory action as well."

Mr Sitoh Yih Pin, chairman of the Government Parliamentary Committee for Transport, said: "It is important that LTA continues to monitor the privately run bike-sharing systems as its implementation progresses and step in with necessary regulation when required."