I have two extra 21" subwoofers. One is blown and needs reconed. The other is brand new never used. Power handling is 1000watts rms, 2000 max for each. I'll sell both for $200, or for $250 I'll build a box for the good one. It would fit well in a suburban, navigator, escalade, ect.
Efficiency is 101dB@1m@1w. You could probably plug this thing into a 100 watt amp and still blow away alot of car subs running 1000 watts.

The one coil was blown because I was accidentally running 2400watts to it.

how well does it sound on the hi-end?

The specs boast that they respond up to 1000Hz and they do, but personally I have never found a need to run them higher than 500.
You can think of it as the ideal speaker for a bass guitar. It will bring out all the sub-harmonics while still hitting the higher notes undiminished and clean. It has a pretty flat response too. You're not going to get a couple notes that are louder than the rest.

Just ordered a recone kit for the blown one, so soon I'll have two working 21" subs for sale. I'll let them both go for $300. If nobody is interested, I might try to incorporate them into my system, but I'm not sure how I'll do that since I don't have any more cargo room in the van.

The recone kit turned out to be the wrong one, but the offer still stands on the good one. I'll put a ready to bump 21" in your' ride for $250. It's not really a car audio speaker (101db@1w@1m), but since it has such a large cone area, it will perform very nice in a sealed box as well.

GONE!! I still have the one that needs reconed. I'll let it go for $50.