I have the Slime pump, and it works great. It's a bit bulkier than the disassembled ones, but the extra protection to the pump is worth it, to me. the .com pump is a generic cheap pump that has had its plastic body removed, but they also gave it some kind of shrink-wrap (it seems). That's to protect your fingers, I suspect. That pump works fine, and I have a similar one, also. It can bite you, it can get hot, and it can be awkward to hold, sometimes. The original plastic body served to guard againt those things.
Bottom line: when you need it, any pump is better than none. The $10 disassembled ones are fine, and when it dies, it's easy and cheap to replace.