I will confess to having a love/hate relationship with this thing.
First is the love. It makes the bike go backwards. That's just wonderful.
The hate is the speed and persnicketyness of the unit.
It's too damn fast. I have to slip the clutch a lot to keep the speed down going backwards. They really need to redesign the gear ratio of this thing. The ratio is right in between 1st and 2nd gear. I'd rather it be 1/2 or even 1/4 of 1st gear ratio.
Once again I had to work on it, to get it to quit dragging the gears. The lever is not locked well on the shaft. When you engage reverse it pulls the gear down, causing the shaft to slip in the engagement lever. Then when you disengage to ride forward, it's only 99% disengaged. You get a slight clacking of gear teeth. Latest fix, that seems to be working for the moment, is red locktite on the shaft.
Lastly, I accidentally engaged reverse while in 1st gear. The world did not end, my transmission did not explode. The bike just didn't move. I went "oh" after a second. Disengaged reverse, got the main transmission into neutral, dropped it into reverse and backed on out. No big deal. And, definitely no need for that engine kill switch.
I have not yet opened up the transmission to drain the oil. I won't be surprised if there's a fair bit of metal filings, from the clacking reverse gear teeth.
If Yelvington ever puts their reverse gear pulley into production, I think I'd much rather have that than the transmission add-on I currently have. A much easier and cleaner installation, and a far better reverse gear ratio. But, the Yelvington reverse still isn't in production, and it's going to be an expensive item.
