I spent hours, days, weeks trying Inbox out over the last few months. I wanted it to work for me, looked for work-arounds for all the repeatable crashes, the bugs and inconsistencies and strange behaviour (you never know what Inbox is really meant to do, as there is not documentation - it may be a bug, it may be a feature)
I was never able to put it to any serious use. Too buggy, too unpredictable.
It looks very nice, and typographically it is well done; the developer may be a real artist, as a developer, he is an unexperienced amateur, to put it mildly.
Beauty can be the icing on an otherwise nice cake; here it is wasted on a wrotten core.
As to the price, it is simply pathetic, this is at best donation ware, no more.
I have been following Inbox from the very beginning, when the developer started to blog about it, to the first release, called a beta when it was not even alpha quality, to 1.0 to 1.1 and a couple of bug fix releases within days of 1.1 which - as usual - was announced during weeks as coming in the next few days and praised as the release to end all bugs and make everybody happy.
And now - again - the developer seems to be completely taken by surprise that once more so any bugs are showing up. He seems immune to learning from past experience - so expect more of the same...
... and save your time and money.