I have an OPEK HVT-600 and also a Sirio Performer 5000 CB antenna which is broadbanded enough to do 10m and 12m as well as its native 11m. It actually works better than the OPEK, but is a bit longer. You assemble it, and leave it alone: no adjustments necessary.
If you want to use the OPEK, you have to unscrew a set screw and extend or retract the whip portion of the OPEK as well as set the jumpers to tune it to whatever band you're wanting--it's intended to be multi-banded, but there is no reason you can't "set it and forget it" for 10m if that's all you want. But it's a bit of a waste doing that--it has options to explore, and if you want to try work from CB (11m) through to 70cm you can do all that with the OPEK (the ICOM IC-706MKIIG goes up to 70cm, from what I can see).
It comes with an Allan key for the whip adjustment; don't drop the Allan key! It's slightly nonstandard (or perhaps just poor manufacturing quality)--if you lose the original, the 5/64 SAE size will work but is a little tight in the set screw.
The antenna "manual" consists of one sheet of paper giving a frequency chart for whip extension (total antenna length, actually) and jumper position. It's pretty close, in my experience, but to get it perfect you'll probably need an antenna analyzer or an SWR meter and expect to spend some time fine-tuning it depending on whereabouts within the 10m band you're wanting to work. The length given in the "manual" is a good starting point, but you might have to fine tune the length a quarter of an inch or so to get it perfect. It really depends on how you're mounting it (I used mine on a magmount on the car).
I found it pretty broadbanded in the 10m band, and even more tolerant at higher frequencies, so you'll have a decent range that you can work. But if you want 20m or 40m later on, it's really rather fussy to use. However, from 11m or 10m up to 70cm, you'll be happy with it.
OH--edited to add: You'll have to think about some sort of ground plane (commercial or home made) or counterpoise in your attic. I've heard of people magmounting the antenna to a pizza tray or cookie sheet, or otherwise providing some sort of ground plane. On my car, the roof fulfilled that function (more or less, not great). Other threads in the CB forum or mobile installation have dealt with that. But getting something decent UNDER your antenna is really key and not to be forgotten.
