I assume you are talking about our Array Wheel Probe, used with our Rapidscan system as well as standard phased array equipment such as the Omniscan, Handyscan and (watch this space)
Performance of the wheel array can be considered as broadly similar to a 6mm monoelement probe of similar frequency with a delay line. If the coating you are looking at could be tested with such a probe than the wheel probe (or an equivalent standard phased array probe ) should work. Its generally like any other UT method, smooth, well-adhering paint or moderate thickness is no problem, If its rough or flaking some work with a wire brush may be called for.
Obviously advantages and disadvantages are specific to the application. I'm comparing it with a standard Phased array probe.
Main advantages are Speed (2-300mm/s with the Rapidscan, maybe 40-50 mm/s with a standard PA unit) and the ability to run smoothly over surfaces with a typical level of surface roughness. In particular this means that the amplitude scan is often clean enough to be useful - helpful if you are looking for back wall irregularity or pitting.
Disadvantages: again application specific, price is a bit higher than that standard PA probe, assuming you are not counting the cost of a scanner. and its bulkier, so not necessarily the probe of choice in restricted spaces. For the right application it gives huge advantages.
Suggest you contact me directly, or talk to your local sales rep, and we will endeavour to answer more detailed questions.