the problem is that there doesn't appear to be any reinforcing frame on the top or bottom; are the acrylic sides siliconed, or 'welded' together? Without something to keep the sides straight, 40 gallons (*) may bow those sides out a lot. I'd want to see this thing filled before buying.
edit: may be closer to 35 gallons acc. to my tank size chart.
All cwt posts are implicitly appended with "just my two cents".