According to RS: 3145 NEW TECH, NEW UPGRADES (the most up-to-date listing of Dark Age tech advancement so far?) the Mechanical Jump Boosters, that wacky curiosity from Solaris, became tournament legal in 3083 (pg.10/11).Thus far, it has not appeared in any canon design- one Juggernaut variant incorporates it, and no one else.
Compared to std jumpjets it's not worth it, but in comparison to improved jumpjets it's a different story. Heavier indeed than IJJ, but taking up much less space. Sort of a compact IJJ. When talking about assault mechs, the extra weight is less problematic; the heavier mechs tend to have more tonnage available than critical slots. In addition, they are somewhat limited compared to jumpjets/IJJ (no facing changes, no DFA).
So, what is everyone's opinion regarding the mechanical jump boosters?