I just got through installing one of thes on a Kona Lanai, typical 24 speed MTB.

Seriously fiddly job, very much a "fitting" process. One of the more serious problems was that the Suntour Crank arm has a little knob on the reverse, (chain catcher?) that was just in the wrong spot and was rubbing against the guard, 3mm bigger hole on the guard, or 3mm further in on the arm, no problem. Just had to be right on the edge. In the end, I took a hacksaw to the knob, unfortunately, I put a small gouge in the edge of the crankarm, will have to watch that for cracks, eventually, I'll get a better set of cranks.

The dérailleur pushes against the guard in top, and causes the crank to rub slightly, I'll either wait to get to work where I have a heat gun and try to form the plastic a little, or grind off some material, may just leave it if it doesn't annoy me too much when riding.

Coverage and durability, I'll say that it looks and feels tough enough to last, SKS has a good rep for that, I might change the self tapping screws that mount it to the back piece for a nut and bolt, you would want to make sure you have enough clearance before doing that. The Front rings are fairly well covered, with full coverage fenders, I'm expecting the chain to stay a lot cleaner, will report when I get to ride in some serious slop. (that won't be long around here) I am going to try finding a small foam disposable plate, and using that to form a cowl for the inner front section of the guard, I should be able to tape it to the inner mount, and tape it to the outer part neatly. This might be considered a bit over the top, but if successful, should really make the shielding very effective at the front.

Coverage at the back is not quite so good, particularly when in the bigger rear cogs, I spent a little while getting the rear mount as close to the small cog as possible, switching the pan head bolt to the inside to give more room and so on, this allows a little more coverage for the chain when on the larger cogs. I'm going to find a suitable piece of plastic to cover the area where the rear tire sprays water on its downward travel to improve things there.

I am fairly satisfied, now, with the fit, I think it's going to seriously improve chain life this Winter. Not the easiest thing to fit, I'm not that good with tools however, your mileage may vary.