A lovely tank space, although I have to agree with Lillefishy on the lid situation.
Despite what a lot of folk say, bettas are indeed jumpers and I personally wouldn't risk it. I do know of some who have similar set ups with bettas in, but one of my boys jumps at dried flakes on the glass if he sees them and I'd just hate to come home to a dead fishy.
What size is the one you were looking at? A quick google shows different sizes at lid types.....