Kustom Force Field, worth it?
The Orks can take a Big Mek as an HQ choice that has a Kustom Force Field which will give all friendly units with a model within 6" a 5+ invulnerable save vs. shooting. If you get clever with your deployment you can have 3 boyz mobs getting this benefit at once, at the cost of having pretty much all your troops in one area of the board and probably making more difficult terrain rolls than you'd like. On the plus side, you'll lose about 1/3 fewer boyz from shooting. The big cost though, is that you've got an 85-point character that can neither take hits nor dish them out. The best configuration would be to give him either a shoota/skorcha kombi-weapon or a burna and then you've got a little more shooting power. However, once the boyz get to assault, this big mek's not got a lot of use. With his T4, 2 wounds, and at best a 4+/5++ save, there's a good chance he won't live long enough to use a powerklaw and even if he uses the burna for a power weapon he's still likely to get stomped flat even by non-assault troops. Against some dedicated assaulters he's definitely a goner. In assault, you'd only be giving your opponent a bunch of VPs.
In order to for the KFF to buy itself back, it needs to prevent 15 or so boyz from dying. That's 45 wounds directed at the boyz. Is that likely to happen in a 1500 point game? If you invested his points in more boyz, you'd be getting about another 10 boyz with a big shoota and nob who has a powerklaw/bosspole. 4 warbikers is another option. If you can find 50 points somewhere, you could even use his HQ slot to take a biker warboss, which are crazy good.
Anyhoo, it's something I'm debating on taking to protect my 2 footslogging shoota boy squads, but it's a lot of points to spend on what amounts to a defensive upgrade for 2 mobs. (cybork bodies would cost 300 points for pretty much the same effect)