Morta pipes tend to be a shade heavier, and seeme to favor English blends. Also, as noted above, the tend to be on the smaller side as the blocks tend to crack as they dry out. They smoke very dry and cool, but the wood seemed to get hotter than briar to me. The grain is fascinating to look at, and they blast really cool. Very uniform in their graining. The smooths don't shine up as much as briar does. More of a matte finish. I've never noticed any burnt rubber or any other noxious taste to them, but the flavor is definately different than briar. More akin to clay or meerschaum. It has the same mineral undertones, IMHO. All in all, great smokes.
Just my two cents.