16x8x21 tank

Someone offered me a rather strange tank which is 16x 8x 21.
Works out to around 10 gal but with a 5 gal foot print unless I'm mistaken.
Do you think this is too small of a foot print for thumbs?
I am not planning on adding thumbs to my small collection for about 6 months but it's a nifty looking tank so I wondered if it would be useable?
Am I right in thinking there isn't enough floor space even for a height loving pair of thumbs?