Having purchased one of those Autorust caps in the past, my opinion would be to get a nice rust-free complete original one from one of the members here.. even if it costs a few $$ more to get it to you.. the ART one is crap.. CRAP
Yes...it takes skills to install the ART caps but they work just fine when installed properly. Our 69 vert can attest to that and they are not made of crap...they can turn into crap if improperly installed though.
That being said, nothing is better than OEM stuff in this case. I agree that you should buy the one that is a few posts ahead of mine.
It's all about convenience and availability of parts as far as the decision to go either way.