Hey, if you have a boatload of long lenses and will be using the Q system extensively with those lenses, and the cost is within your budget - the Pentax unit with electronic shutter is the way to go.
If you plan to adapt lenses occasionally, plan to primarily shoot lenses handheld at 100mm or less, are on a limited budget, and are willing to spend 10 minutes painting the inside of the Fotodiox with $4 worth of matte model paint, then the cheaper alternative will work just fine. Certainly at the minimal cost (under $40) it is worth investigating, even if you might ultimately go with the OEM unit.
Personally, I have little need for extreme telephoto (my 85mm yields about 475 equivalence and I'm not going for more reach than that - and rarely encounter any rolling shutter effect with that length).
Overall, I think c-mount options are even more interesting - as many varieties are available, the small package remains tidy, the sensor match is better, and results can be optically excellent even at a minimum investment if you spend judiciously.
For under $30 you can get a good, new, all-metal lens that looks like a proper fit on a Q, and high quality adjustable metal adapter - yielding results like this: