I think of it, the idea of a Jem MK XII space set upgrade was well worth it before there was a Adapted MACO MK XII space set (seeing it was an Honor Guard light). I'm still eventually going to get it (cross my fingers), its a nice add on to a Bug using Polaron.
Hi, my name is: Elim Garak, Former Cardassian Oppressor
LTS, here since...when did this game launch again?
It's worth it if you're interested in PVP. The Jem'Hadar deflector is a great choice for power draining builds, as well as other sci-focused builds, and the +2% stealth detection provides a not insignificant boost to tachyon field and sensor scan and that sort of thing.
The shield is very nearly on par with the MACO XII- the only real difference is that it loses out approximately 400 cap and doesn't have the +power ability- instead it gives +10 kinetic resist and + able crewman resistance, so your crew don't get injured as much- which translates to basically a saved engineering console slot (No need to run emergency forcefields), so you'll benefit from having a human crew boosting your repair rate longer.
Perhaps the most universally useful of the set however are the engines, which provide a static +5 to weapons power, and also have a 'efficient weapons' bonus that grants a variable of up to +7.5 additional weapons power, depending on your weapon power setting. Thus if your weapon power is set to, say, 25 (because you're running a carrier or a sci ship and aren't as focused on direct damage), you'll see a net boost of +7.5 power, raising your weapons power up to at least 32- and more with training in warp core efficiency and warp core potential, both of which provide bonus power.
The main downside to the Jem'Hadar set is that it doesn't quite stack up to the Omega rep sets in ancillary abilities- the damage boost to Polaron weapons is nice, but it doesn't have the versatility of Tetryon Glider. The 3 piece bonus is much shorter range than either gravitic anchor or the maco ability, and does much less (just drains shields and decloaks unlucky ships), as opposed to knocking subsystems offline, pushing the target, and inflicting a massive defense penalty.
As a result, you have a set that is strong, but it is not the best choice for most builds- the Borg/MACO/OMEGA/ADAPTED sets are.
It *is* a very solid choice however for some builds, and if you're going to be flying one of those, then chances are it's worth the effort in buying a bunch of keys off the exchange to get the lobi for it.
I found the set to be worth it. The simple truth is that there really aren't very many sets better than it is in general. The ones that are require a lot of grinding and many days worth of reputation missions before you'll ever see them. In the interim, the JHMXII set provides the player with some useful bonuses that will serve them well until they decide to invest the time into something better. It's absolutely a step up from the MK XI set. If you've already got access to the MKXII maco and omega sets, then it will offer less utility overall.
So, honestly, how worthwhile it is seems to be dependent upon how easily you can acquire better sets or if you find the bonuses suitable to your build.