For one, there is this weird way of selecting calendar items (including the hours). First click starts the selection process, then second click finishes it. Very unintuitive. Especially confusing when trying to manage the booking form in the backend.
Saving the changes to multiple selections also takes a while. And it doesn't save properly either. Changes applied for a whole month resulted with one week not being available, yet everything else in that month saved ok. It seems I have to press "reset" before applying any changes (but that doesn't work 100% of the time either). And the "reset" button then jumps a month ahead for some reason and I am not able to return to the current month without refreshing the whole page. Maybe this is how it's supposed to work and I'm just missing something, but the interface does seem a little over complicated and buggy.
Once the reservations are made, in the backend there is a little number on the envelope letting you know there's a new reservation. Well,.. it doesn't actually disappear once you approve it. When you get 10+ reservations, it starts being a job in itself just to check which ones have been approved and which ones haven't. Imagine there were 50+ reservations!
I'm sure some more testing would result in more bugs. Too bad. It's a neat little calendar. I like it a lot. But it's not prime time ready. It's v0.5 I'd say.