I have also run both styles.
Pros on the TKI - Can adjust gear ratios to dial in exactly what you want. Easy to put belt on.
Cons on the TKI - I bent/broke three tensioner arms which ruined days of riding. I've had friends bend tensioner arms which also ruined days of riding. The lower pulley clearances on the driveshaft were sloppy causing the pulley to rock slightly breaking the bolt head off which also ruined a day of riding.
Pros on Kurt's kit - Simple gear down and the clutch kit works great with it. No screwing around tuning the gearing and clutching. Put it in and have fun instantly. Has not ruined any days of riding for me.
Cons on the Kurts - Not a huge deal because it comes with install tools, but the belt is tougher to get on.
I agree with Travis!!!
A couple of summers ago, I replaced the QD and ORIGINAL belt on my Pro at 2400 miles. My track is the Camo X3 x 156" track (7t 3.0 pitch Avids).
I bought my TKI used...from either Travis or Tory (I can't remember now, HAHA).
It was bolt on and go. I liked that for my Pro because I had changed drivers and track and wanted to pick a specific ratio to suit my build. I liked the idea of having the tensioner for swapping gears on and off...but I've never pulled them off, so in the end, it was a benefit that I never utilized.
I still have that sled and I still have the TKI on it. Has over 1200 miles on the TKI now.
This year, I ran my stock QD on my 19 850 for about 450 miles and then decided to go with Kurt's Gear Down. Bolt on and go. I have one ride on it....and it's been great so far. No gearing options, but after not needing to change the TKI gears on my Pro's TKI, I'm not anticipating that I'll need to on this chassis either.
I think this ratio is a good one for my BD boosted 162 x 3.2" track (7t, 3.0 pitch Avids). Clutches are cooler and it's got a little more grunt on the bottom.
I made steep pulls last weekend in deep SOFT spring mushy powder with 63mph track speed. With the gear down, I think I'm going up the hill with more track and ground speed than when I had stock gearing.
As a side note...(I like Tom and he makes really great products, so I have no beef whatsoever. I'm a fan)
I have been told that belt tensioners create a parasitic loss of HP. I haven't seen dyno sheets to prove either way so I can't verify that.
BUT, it does make sense to me. I have seen dyno sheets that compared track tension. Tracks did have more HP loss when they were too loose or too tight. They did best when tightened to specific factory specs.