I wasn't completely pleased with the Tippi. Didn't slice that well for me when I bought it a couple of years ago.
I've been very happy (for about 12 years) with one of the original Hot Wire Foam Factory units. Used it to build both my layouts. So far, I've created almost 40' of stone retaining walls, dozens of tunnel portals, rock cliffs, scenery, etc.. You can vary the heat of the cutting wire which is important.
JMHO,