Few deny that these booking apps are welcome new tools. Now you can book a hotel at the last minute without the hassle of using a computer, but the best deals may lie elsewhere.

New applications for US smartphones are giving travellers an edge in booking hotels on the fly. But while these mobile tools deliver last-minute convenience, they also bring the potential to push consumers into excess spending.

This spring, travel companies are launching a spate of hotel booking apps. Today, for example, months-old app HotelTonight relaunched in an expanded version (for Apple devices only). Until now, the tool only let users book for a single night's stay in a couple of cities. But now the app lets you book stays of up to five nights in eight major US cities, including Boston, Chicago, Los Angeles, Miami, New York City, San Francisco, Seattle and Washington DC. The app has been downloaded a quarter of million times since its January launch.

Meanwhile, as The Passport has reported, industry giant Expedia is also jumping into the mobile hotel booking game with Apple and Android versions debuting this month. All of these apps join existing tools by Priceline, Travelocity, Kayak, and Hotels.com, reports All Things Digital.

Many of these apps have perks that online sites lack. HotelTonight, for instance, lets you book as late as 2 am for same-night arrival, which Web-browser based sites like Orbitz don't let you do consistently. Meanwhile, Expedia's upcoming booking app will copy HotelTonight's trick of recognizing your location by using your the GPS-feature of your device, recommending properties that are most relevant according to your location. That's a major perk that browser-based Web agencies lack.

That said, there are several downsides to hotel booking apps.

Since 2003, many major hotel chains have offered price guarantees. Book directly through their own sites and you're assured the lowest rates for rooms available online. If you find a better deal on another site, you'll be refunded the difference plus given a small room credit of about 10%. But these price guarantees only apply to rates found on other websites. You'll have to book through browser-based sites to grab the bargains.

Mobile apps open up a whole new field, not yet covered by guarantees. HotelTonight doesn't make any guarantees about offering the cheapest rates available and Expedia is still reviewing its long-term pricing strategy for its upcoming booking app.

Mobile technology gives hotels the capacity to withdraw promotions as soon as they've hit their quotas. This prompts consumers to book quickly without much comparison shopping.

Booking on a phone or tablet, with its tiny screen and limited range of browser windows may force some travellers to book before they've had a chance to suss out whether an advertised "deal" truly is one.

Honing in on the best deal isn't as simple as looking for the lowest nightly rate either. Hotel marketers often flog supplementary perks that have real dollar value. Instead of lowering room rates, they promise free nights, free room upgrades and more. That means pitfalls for travellers who don't shop around.

The news isn't all bad on the pricing front, of course. Especially at the start, you might see promotional sales on mobile apps that you can't find elsewhere. But in the long run, consumers will see higher rates on apps than on their favourite travel sites.