I have only had positive experiences with Ancor Marine 4 AWG to 4/0 AWG tinned cable. Even the off-brands struggle with matching their prices, while falling far short in matching their quality.
For what it's worth, we sell Ancor marine-grade cable by the foot (it's hard justifying 25' of 4/0 from Amazon). I can personally recommend the Ancor line, as it's all I'll use on my own personal projects including rewiring my truck as well as my 200Ah LFP at-home battery back up system. Really the highest-grade tinned wire you can come by. As far as I can tell, though, our prices are right in line (within a few cents) of Greg's Marine referenced above, so *shrug* six of one, half dozen of the other!
I'm no expert like some here. But, after listening to everyone and weighing the pros and cons, I found them to be up there with the best in quality, and are unbeatable in price. I talked to them before ordering. Very helpful. From everything I can see after receiving, very quality job... much better than I could ever achieve if I ran out and bought all the tools needed. They shipped quickly. I couldn't be happier so far. Of course, only time is the true test.
They are also from KY. I love that region of the US for this sort of things. Ever since I met a lot of crazy engine building people from WV, I discovered they really really love building things by hand and are into all the hard stuff. It's a culture there. So, I felt better buying from that region of the US.
I'd give them 5 stars if there was a way to rate them. Let us know if you are as happy.