Got one, love it, wouldn't trade it for anything! It's so light Kody thinks he's grown wings and it turns on a dime so the horses LOVE to spin it at high speed. I much prefer the ride with the pneumatic tires as it's much smoother but it's okay with the solid rubber rims I have to use for Preliminary competition too. I had no problems with shoulder rubbing or equine discomfort when I used it without a singletree for the first couple of years but do prefer the ride with the newly available singletree (it absorbs any jolts better). I also like the available seat slider as it makes it possible to have many people using the same cart without messing up the balance.
Downsides- can't take passengers, awkward to get at anything tucked in the various attachable bags while driving, you look a little funny sitting right up there on the horse's rump, you'll need a shorter whip and possibly shorter lines as well.
Pluses- Total freedom to go anywhere at any speed with no fear of tipping over or coming out of the cart assuming you've correctly adjusted everything. Horse loves it. Manufacturer cannot be beat, stands behind his product 110%. Ongoing customer service is fantastic. The Hyperbike has been tested into the ground and will not break or fall apart on you or Bob will know the reason why AND fix it.
It can be disassembled in minutes with no tools and fits easily in the trunk of a car.
I really do love mine. It's incredibly stable on rough terrain and the horses think it's just the coolest thing since baled hay. I drove my show cart in roadster configuration recently and felt SO insecure by comparison! It was like I was going to bounce out at any minute and now and then the stirrup would suddenly drop out from under my foot with no warning. Ugh! Noooo, thank you. I'll take my Hyperbike.
Leia