Yesterday I tested a recent (but well broken in) Jensen C12Q reissue speaker in my 5F2H harp amp. I installed the Jensen speaker and played it without having played any other amp or speaker before, to avoid biasing my ear.
The tone was oddly flat... not objectionable, but just not lively. Another musician listening described it as "dead." It did get a little bit of rip on the big harp notes, but the speaker did not seem very loud. Jensen claims its efficiency rating is 94.6 db at 1/watt 1/meter, which is rather low.
The tone spectrum was mostly mid-lows. Definition was a bit muddy. As I say, it was not objectionable at all, just not inspiring. I played it for about an hour, trying various volume and tone settings on the amp. I didn't find a "sweet spot" for the C12Q. I was using my usual Shure CM-equipped bullet mic with no pedals or effects.
It is possible the Jensen C12Q would sound better in a different amp. But the 5F2H is a pretty good test bed for speakers because of its ultra-simple Class A design.
One very positive thing I can say about it is that it had zero ghost notes, something I've found to be a problem in 12-inch guitar speakers used for blues harp. The Jensen reminded me of many harp amps I've heard -- both harp-specific amps and converted guitar guitar amps -- that lack the projection and definition I like in harp tone.
Incidentally, the Jensen C12Q is one of my favorite speakers for guitar but it just doesn't tickle my happy zone for harp. I can't recommend it.