The OT7 is not even close to the capabilities of a tablet. Many of the OT7 functions don't work properly (at least not yet), new features have been released that don't work, so in an lemon to an apple comparison, the OT7 offers simple SnapLink functionality (today), and having a tablet running any other app is like having apple pie made with apples, with access to more features and functions that currently working on the OT7.
As example; a tablet's VoIP app can connect to H.264 cameras and stream audio and video. The OT7 is limited and does not currently support H.264 for cameras.
As example; a tablet will support intercom features with most any IP video intercom devices, not limited like the OT7 and the OT7 has yet to perform that function reliably with the three (3) approved intercom models anyway (including the new Leviton model), if at all, plus OT7 requires a separate SIP server (at addition expense)
As example; a tablet running SnapLink can access all the other functions the OT7 offers with exception to BEEP. The Beep function, which unfortunately is also not reliable on the OT7 (depending on firmware version), is however not available in SnapLink.
As example; a tablet running SnapLink also does not have access to "Rooms" that the OT7 offers and while the "Rooms" appearances behave strangely (depending on firmware version), Rooms is convenient.
As example; a tablet running SnapLink would allow you to use a PIN code to secure the panel, the OT7 has NO security feature so all functions are fully available.
FYI... the OT7 is a rebranded Android tablet, however, once all the functions are fixed, I believe the OT7 will be a nice compliment for most any installation. Of course Space has gotten some bad reviews in iTunes too, but you would hope with some time those issues will be resolved as well, although as ano said, the author has been full of promises that have fallen short time and time again. The HAI OPII system is some fairly old technology and it looks like Leviton is moving towards Lumina Bitwise. From that, we could "assume" a few more years of use plus the OPII hardware should continue to run for many many years anyway - you might however not have any working apps as Android, IOS, and other operating systems are modernized the old apps will become incompatible without updates, so that is the greatest risk you should consider. Investing in tablets for in-wall controls would then seem to make better sense for now due to the cost savings and functional access they provide and they can be used for other things should the automation need ever change. I'm still hoping to see some OT7 updates that make it work reliably.