First off, they add +30% breakthrough off equipment. Mountaineers (and SF in general) are more offensively orientated tools. SF get the smallest defensive boosts from the support weapon upgrades (which means the infantry will have more, which means more e-org), and depending what doctrine you choose, the bonus org/recovery that the SF gets might become much less of a factor. Your basic infantry are going to be doing basically the same thing, without the added complexity. Not that the SF cap matters, there are lots of exploits to get around it. I suppose you also get the higher org and recovery, and perhaps a pittance of attacks depending on your techs, but I don't think those are worth the cost of HP ratios, IC cost, and eating up your SF cap. There is little point in using mountaineers defensively, you're only getting +10% in mountains or +5% in hills. But if you have no choice but to actually push through the mountains, a mountain fighting division will usually help. Or to first encircle the enemy on the mountain and starve them down, to minimize the amount of fighting you actually have to do. It is often a lot easier to simply go around a mountain than it is to try and fight through the mountain. And then you have to ask what alternatives there are that might be easier, or more effective. First off, you have to identify what your problem actually is that you are trying to solve it with designing and fielding a whole new type of division.
