I have not seen any apps (including our own!) that are sufficient for GMAT prep on their own, no.
Apps are typically designed to give you good practice - but they aren't typically designed to give you comprehensive lessons, nor will they replace taking full-length, GMAT-format practice tests.
Further, an app that is designed to be used on a phone will be unable to give you access to certain things in true GMAT-format. RC is impossible to do in regular format on such a small screen. SC is difficult - it's much harder to compare the answers vertically when the answers are compressed into much shorter lines. For longer problems, you can't even see all the test at once but have to scroll. Most apps don't have the capability to provide the interactive functions of IR questions. I could go on.
Apps are great for squeezing in on-the-go practice - while at work, etc. They can be a good supplement to your studies if you like the form factor and you want to have something easily accessible for 5 to 15 minute bursts throughout your day. But (at this point anyway!) they shouldn't be your main source of study, no.
(Also, regarding completely free resources: it is difficult to write quality practice problems - it takes a lot of time, and time is money. You should be able to try out apps / have
some free content in order to decide whether you want to buy. But if you want very high-quality study materials...be aware that it's less likely that a completely free app / product is also going to be very high quality. The costs are high enough that you can't just make it back on ads. It would make a good business case study, actually.
)