The Poser things that will not work are:

a) Poser dynamic clothing (as noted above) - not at all

b) Clothing with Poser shaders - the colours will look funny in Daz Studio but you can compensate using the Surfaces tab or if you have bought some Daz Shaders you can use those. This is the most common incompatibility but its inconvenient rather than a disaster. So if you see something where you really like the geometry its probably worth buying but be prepared to compensate for the textures.

c) Things needing Python scripts - won't work at all.

d) Older Poser characters like Miki2 will work in Daz Studio. New Poser characters e.g Poser 9 on will not but, especially if you have just started out, no need to explore Poser characters. They are not that good and its just novelty.

To be honest that common phrase 'not tested in Daz Studio' irritates the hell out of me because Daz Studio tries hard to allow Poser users to use their items but its not reciprocated.