I have 4 of them, and in need of 2 more. Some of my betta's use them some don't. However, I like giving them the option to have a place close to the surface they can rest at.
It fits in a 2.5 gallon tank, but does take up some room. I had one in my 2.5g though for a long time.
My guy loves his. My only objections are that if you have a filter it gets pushed to the far side of the tank. Not a big deal.
But if you don't have a filter like me, it floats around and scuffs up the tank walls a bit. Avoid this by setting it between some plants.
Overall its a great product. Some are known to sink but just take it out and airdry it and set it back in.
I know it costs like around $10 a pop but if you search online, maybe you can get it for a cheaper deal. I got like 6 of them for like $2 or $3 each at one point. I got it at Pet solutions and I don't know if they still have that sale or not. Well good luck with that. I have a 20, 10, 2.5 and some kritter keepers. Bye.