I have a one step looper, and I love it. There is a 'knack' to using it though, and I would suggest a root around utube to see how others get the best out of it.
It is really nice for getting a professional look when you want all the eyepins to be the same size in a wired item. The loop it makes is smaller than your average eyepin that you buy, not really a disadvantage, but something you should be aware of.
If you are using it to encase a bead with a loop at either end, you don't get a totally snug fit, as you would if you were doing a wire wrapped loop at either end of the bead, at least I haven't been able to manage it yet, but the spacing is even so looks fine.
Worth getting one if you use a lot of different coloured wires and need matching eyepins, or enjoy making the 'rosary' style necklace. If you can think of lots of things you do with eyepins then this is for you. If you don't use loads, then remember, the money you spend on this tool can buy quite a few eyepins and other findings.
Hope this helps...
Hugs, Janie xxx