We have the Solo Bonfire. Definitely do not go smaller. We have trouble with some of the firewood not fitting in the Bonfire, but the next one up was really heavy.
One thing we notice (not necessarily unique to the Solo) is that while the fire puts out a lot of heat, it is all "above the rim", so the sides, while hot enough to burn if you touch them, don't radiate heat. We had a raging fire going last night, but I used a blanket to keep my legs warm.
It does burn down really well, so minimal ashes. It also goes out fairly quickly once you stop feeding it, so we are not staying up to wait for it to go out (you can't put water on it). We also bought a metal trash can lid to cover it at night so that we can leave it out to cool and make sure it is out, but not get wet if it rains.
Prior to this we had the generic wood fire pit from Lowes that would last 18-24 months before rusting out at the bottom. This is an improvement for sure.
Mama to three boys ('03, '05, '07)