CZ sights and frames
Sights are a problem with many of the new CZs -- as there aren't many after-market providers.
The old CZs used a "staked" front sight, while the new ones (on most models) use a lengthwise dovetail. You don't just install ANY front sight on the new CZ guns, and you can't just cut a new dovetail.
Frames on the newer CZs (the "B" guns) are NOT forged, as suggested above, but cast. CZ prides itself in being one of the world's most- technologically sophisticated gun makers in its use of new computer-controlled- and metal casting technologies. The guns are very good.
The only reason I'd get a P-9 over a CZ, at comparable prices, is that I've got a bunch of CZs, and no P-9. (A new CZ, howevere, comes with a warranty.)
The CLONES aren't really clones in the common use of the word (as in "1911 clone"). They are all derived form the same basic design, but that's like saying a Corvette is a "clone" of the Camaro (or vice versa).
All of the Tanfoglio guns have substantial changes in design -- many to simplify production -- with very limited parts interchangeability with CZs.
Basic things like barrels won't interchange in most of them -- as Tanfoglio uses the same (outside diameter) barrels on their 9mms and .40s, while CZ uses different diameters for each.
You can, as noted above, often swap top-ends; but things like safeties or decockers may not work properly.
The inner mechanisms in the frames are subtly different, from simple things like the safety design, to how the hammer spring works, to the firing pin and firing pin safety mechanism, or the presence or absence of a mag break/mag retention spring. With most CZs, the mag release is not reversible; for most clones it is. Even mags won't always interchange properly -- as the EAA guns have their mag release set a bit LOWER in the grip than do CZs.
The "clones" and CZs are all good guns.
There are many more after-market parts/enhancements available for the Tanfoglio/EAA guns than CZs -- because of EAA's long involvement in IPSC, internationally. There are a LOT of EAA race guns floating around.