Has anyone use these spools? How are they? I heard you can only use PE line with them due to the fact that flouro can  cause the spool to cave in. But also heard some people say if you put it on very loosely it’s fine.

A friend has a pair of KKR spools and likes them both, T-31M and T-37 long-cast SV.  

 

He fishes 0.15-mm braid on both.  Yes, at 4 g total weight, I'd think there's not a lot of metal thickness there, but it ought to sail light baits.  

 

To me, threadline braid is the reason to fish these spools.  

Ray's Studio offers "long cast" deeper spools for mono.  

Avail also recently came out with their first Daiwa spool -34-mm for Steez/Zillion - that's plenty stout for mono.  I expect they will get around to a 32-mm Alphas spool.  

 

That said, you can probably get by with 4- and 6-lb mono on the KKR spool.  

If you end the day on a cast instead of a big bass, I wouldn't worry too much about mono-relaxation crushing the spool.  

I wouldn’t spool loosely as this will typically cause backlash. I just got mine yesterday. Also looking for input. Send there isn’t any reviews on it yet. Google only provides purchase point links. Haven’t thrown anything yet but plan on doing so ASAP.