While it's not the greatest cartridge ever invented I've had the 4S chambering since early '13 and a 6.5x300 saum since '08 and I really like it. I've yet to kill anything bigger than deer sized game but others have killed elk and moose with the cartridge. It's certainly not the be all end all but all things considered, I think it is the best overall 6.5 cartridge available. That is just my opinion, so take it for what it's worth. Would be made better if there were a steady supply of the brass for it.
The 6.5x300 was a good cartridge but the 4S provided much better brass life. I would only get 3-4 firings on Rem brass with the 140 VLD and I am now at 9 reloads on the same 100 pieces with the 4S chambering pushing them at 3110 fps out of a 25" Krieger. That barrel is currently at 2800+ rounds and still shooting well (consistent .5-.7 moa). Other guys have similar experiences (and better) with the brass and barrel life. I'm currently using H1000 and the 140 VLD but I've shot the 130 VLD, 130 Accubond, and 129gr Hornady SST and all shot well. I've also worked up loads using R-22 and Retumbo when H1000 was scarce and my gun shot everything I put through it really well.
The crux of the cartridge is brass and ammunition. If you don't reload the only option I know of is Copper Creek. Folks have had good luck with their product but in my opinion it is super expensive when there are other calibers that will suffice. GAP just recently ordered 100k pieces of headstamped Hornady brass but it sold out in about a day. More is supposedly on the way but the way the first 100k sold I'm glad to have my original 100 still holding up.
Remington, Norma, Nosler brass can be worked up for it by simply necking down 300 or 7 saum brass and turning the necks. Not hard, but not straight forward reloading and probably not for a beginner in reloading.
If what you are mostly doing is hunting with it and not shooting a high volume at targets I would probably go with a caliber that has quality factory ammo more readily available. If you are a seasoned reloader, shoot target practice quite often for fun, and want to try something different I think it is a nice choice.
