Before buying from the big guys, go to harbor frieght if you have one locally and see what they have. If I had gone there first I could have saved myself alot of money on all the heat shrink stuff. HF had almost everything I already bought for about 1/3rd the price. I bought extras from them and have used them since when wiring my TM, I didn't notice a difference in quality.
I have used a bunch of the Harbor freight Marine heat shrink. I was expecting come crap that wouldn't work and was surprised at how good it was. That and a $12 heat gun and now my wiring jobs look alot better.
I order mine from this guy.
Email him and he will give you his phone number to call him direct without going through ebay.
IMO quality of the HS butt connector doesn't matter .When you crimp them with cheap crimper tools you always end up cracking them anyway thus allowing moisture into the connection.
My method is crimp, heatshrink, apply 5 minute epoxy over the whole connection to seal the cracked crimp and ends of butt connector. Lastly slide heat shrink tubing over the still wet epoxied connector and shrink it. I do them like this on everything including my trailer and never had one go bad.