The problem is, any squonker can only be as good as the atomizer you put on top of it. So, find something as close to your favorite rda with a bottom feed pin as you can get.I know the Coppervape looks really nice, inexpensive, but then you need to get your own topper. I guess I looks at the Pico squonker as more of a test device of "will I even like the whole squonk lifestyle?". I'm sure if I do I'd get a different topper and probably a different squonker as well, but the low entry price of the Pico Squeeze means no kicking myself on something that ends up in the back of the drawer if it bombs (along with other stuff like that).
There are some differences though depending on how you vape. Not all bf atties are made equal.
I have a velocity(v2 I think) that came with a bf pin, it's a great cloud chucking atty, if that's your thing, but it SUCKS for bf. The reason why it sucks is, the bf pin comes up from the deck a few mm, so it doesn't drain at all. That's not so much of a problem if you like putting lots of cotton in your RDAs, but that kind of defeats the purpose IMO. I prefer small chamber rda's, and I use as little wick as I can possibly get away with. This means I need something that I can "over-squonk" that will drain back down. A deep well on a bf atty is a waste. Bottom airflow, though some like it, will probably cause leaking issues.
My all time favorite is a derringer, but they have to be converted. The RM2 from REO is great for single coil, but you have to drill out the air hole. I think the derringer V3 can be converted by just swapping out the center pin with a bf center pin, but I'm not sure on that.