As a DIY speaker builder, I've logged many hours building & tweaking crossovers, and one big compromise of a 3-way design is the HP filter you have to put on the midrange. This is, at the very least a large capacitor to roll off at ~350 Hz, plus a large inductor too for a 2nd order. These components are now in the signal path of your crucial midrange frequencies, and they're also affecting the phase alignment of the midrange with the tweeter. You may also need to invert the polarity of the mid driver (or not)... it just depends on other parts of the design. The 2.5-way design has fewer crossover components in the way of the midrange, and has more low end capability than just a 2-way. There still will be some phasey issues between the 2 woofers as the lower woofer rolls in to align with the upper woofer. I admire the idea, but I've never built or owned a 2.5 way design.