Does anyone have a high end Shimano spinning reel that features this? I'm curious if it actually significantly increases casting distance or is just a bunch of hype? It sounds good in theory but might be just another marketing ploy. 

I haven't done any scientific measurements but it does add noticable casting distance. Granted I'm comparing a miravel with short stroke spool and cheapish sufix 832 braid to an exsence with every feature offered and PEX8 braid. Comparison was done with the same rod/leader/bait.

It takes a lot longer to get deep into the spool so I think line just comes off the lip more efficiently.

I use my Shimano high end spinning reel to fish for shad in Spring.  I've used other Shimano reels also.  This is to cast a shad dart that is very small (1/8 oz or lighter) and I get at least ten feet more with the Infinity Loop feature.  I use the same line test and make ( mono) and the same rod and lures. I also get less tangles with mono.  The line seems ''flatter'' and more even on the spool

I have a Vanquish but it's on a NRX+ 852S.

 

It's a terrible rod for casting and regret buying it.

 

So yeah, I have one, but I can't really give an opinion on it.

All my spinners are Shimano worm-drive '19 to '21 - couldn't pry any from my cold fingers, etc.