I wanted to update this thread now that I've had this rack for a couple of months. I use it exclusively with my road bike for good weather riding when I don't need to carry a lot of stuff to work with me. Since I did not want a permanent rack on my road bike (it's my only bike without a rear rack and fenders) this offered me an option to carry something to work without having to resort to a backpack. I already had an Arkel Tail Rider so it made the marginal cost more tolerable. Incidentally, Arkel just sent out a newsletter for 15% off the Tail Rider and/or the rack using coupon code ARKELTR11 (but only for the first 100 sales).
Fitted onto my Jamis Quest, the rack occupied the existing space of my saddle bag mount which had to be removed to make room for the bracket to fit. It takes less than a minute to fit the rack or remove it for leisure rides when it's not necessary. Since I carry a Dinotte tail light mounted to my saddle bag normally I had to zip tie a piece of plastic tubing to the exterior of the Tail Rider to serve as a light mount. That serves as my rear light for the ride home since it gets dark before I leave work nowadays.
The overall set-up is very stable and with the rack attached to the saddle and stabilized by the seatpost it feels very secure. I would not hang anything off the sides of this set-up though as there are no side stays which would keep things away from your wheel. There is no sway that I can tell with the rack even during climbs with the Tail Rider loaded moderately full with an extra shirt, my saddle bag (with tools, tube, etc.), plus a Magic Shine and the Dinotte tail light and a cable lock. I could have fit a light lunch into the bag as well.
Overall, if you're ever wanting to ride your non-commuting bike to work and you don't have that heavy of a load to bring with you to work this could serve as a viable alternative for a full rack set-up. I'd buy it again but it is much more pricey than a cheap rear rack + cheap pannier.