I'm sure there are much more knowledgeable people in the community than me and who own Islander's and have done business with Mark from Long Island Watch (LIW), so I'll definitely defer to them regarding your question. That caveat being said, hopefully, the below helps.

Islander Watches are Mark's own brand of watches. from what I understand, Mark was originally just a retailer for brands like Seiko, Orient, Demasko Squale etc, but when Seiko decided to discontinue the SKX (the best seller for LIW), Mark decided to make his own brand of watch that could improve on the negatives of the SKX (ie Hardlex crystal and a non hacking movement). The early watches for the brand were incredibly successful and there are now dozens of models that are both homage's to watches like Seiko, but also some original ones. 

Islander watches are also made in China (like Chinese brands such as San Martin), but as you said, LIW is a US based business, so any issues and you're dealing with Mark and his American team, rather than a Chinese company. Most brands on AliExpress the customer service is pretty ordinary, that said, established brands like San Martin are usually pretty good.

Whilst I personally haven't bought a watch from Mark... so I can't talk about the quality of Islander watches, what I can say is that they have been made for a few years now and Mark's LIW business has been going for nearly 2 decades I think. So they're not a fly by night brand.

If you're worried about after sale service, I'd suggest Islander watches over any AliExpress brand.

Cheers