Different beasts in my mind - the solo is a woodgas burner where as the Littlebug is really just a pot stand. That's not being derogatory mind as I like the simplicity. I've not used the Solo but have used a couple of other woodgas burners, they are good fun and I like the one I have but it's quite a bit of faff to get it going well and a bit tricky to recharge with a pot on (this looks less of an issue with Littlebug). Also it takes up the whole of my billy (Mors Pot) with not a lot of room for anything else where as the Littlebug looks like it breaks down very efficiently.
Between the two I'm pushed towards the simplicity of the Littlebug, sure it's less efficient than a woodgas but TBH that's not really an issue as fuel is usually plentiful.