To your orignal question, no, you won't have any issues if you squeeze the jacket on the cable a bit. There is still the proper gauge inside and you will be fine.
Also, be sure not to run the wire you have inside of walls, it is not rated for in-wall use. All in-wall cables must have an exterior jacket on it.
I will say that I've used this type of banana plug and I don't like them at all. I looked at the Sewell stuff and I'm just not overly impressed with what I've seen.
This is what I like most:
Nakamichi plugs 0534B, Nakamichi connectors, banana plug, RCA plug, Nakamichiplug.com , Nakamichi Audio Speaker Banana Plug connector, Nakamichi plug, Nakamichi connector
They provide a double set-screw type connection which completely locks the wire in securely and easily with a shielded shell which helps to prevent shorts. Very easy and very secure at the right price.