In-box measurements of MCM 53-5165http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-53-5165-/53-5165
Surface mounted in a Denovo 0.23 cubic foot enclosurehttp://www.parts-express.com/denovo-audio-knock-down-mdf-023-cu-ft-mini-bookshelf-speaker-cabinet--300-7062
Mounted on center axis, about 8" or so from bottom.
Distortion, SPL accurate, 1M:Extremely
clean above 3K, and still very usable at 2K (with careful crossover work). However - that dip at ~3K is fairly pronounced and may be a turn-off for some people. It doesn't bother me since it falls right in the region that always sounds just fine with a dip. Slightly elevated top end, however, may lend some slight sizzle - but given the pretty much non-existent distortion in that area it will sound cleaner and more natural than the slight rise would otherwise indicate.
Before anyone gets too excited about that dip, however - keep in mind this is a metal dome and as such, has a phase shield implemented. So, let us take a look at the off-axis:
That is out to about 30 degrees or so - seems to be a natural for a sloped baffle.
That being said, if you use this tweeter - keep in mind that the dip at 3K will fill in off-axis, and trying to "fix it" in the crossover to get to a flat on-axis response will probably yield some pretty mediocre results so leave it in there - physics will take care of it. The top couple octaves smooth out nicely just a bit off-axis, as well. This tweeter will probably be great for speakers with a wide spacing and no toe-in.
Speaking of off-axis, some additional evidence for why we don't trust polar models:
The breakup is not predictable using standard simulators, and in this case for maximum effect will require quite a bit of tanking - or at a minimum a dedicated notch at 8500 in addition to whatever other crossover you are using.