I did my first ride last night using the latest generation MBA with Yosemite, and I would echo your sentiments exactly. The frame rate was a bit slow and choppy, but I expected this and it was totally usable. I had the laptop mirrored to a 40" TV via HDMI and I was pleasantly surprised how well it worked.
I also thought something to signify the start of the KOM and Sprint would have been nice.
I also thought it was a little odd that the little marker map on the right side of the screen moved from right to left.
Lastly, I thought it was odd that at the end of the ride when “I’m Done” was clicked the app just seemed to crash and close, rather than going back to some sort of a stats or profile page. I would rather the app close with a command Q instead of just an auto shut down.
Just finished my first ride on the island with a Mid-2011 13" MBA using Intel HD Graphics 3000. I found the results pretty darn good with no choppyness at all. I wish I had a better machine to compare it too as I’m sure I’m missing a bunch of stuff but it is totally usable and I wish I could have spent more time riding. Will hit it again tomorrow for my normal training ride.