This is a brawler. Your purpose is to get in close with the enemy, and pound them to dust. With 80 MRM's slamming into their mech, that doesn't take long. Your preferred targets are assault mechs, as you'll hit them with your entire salvo. Ghost heat does exist if you fire both your MRMs at once, but it's the difference between 24.61 and 23 heat, so it's certainly not deal-breaking. I prefer to have my MRM's on opposite sides of my mech, that way, when I corner, I can shoot them off seperately as they come around the bend. I find that if I get myself into a target rich environment I can overheat myself, but this typically happens when I'm doing something stupid, like trying to take on the entire enemy team by myself. In a dual my opponent generally doesn't like getting MRM's nonstop, and with him running away like a little girl I can't shoot non-stop, and this means I don't have much problems with heat. Why the LRM 10? Well, I find that the beginning of the match is often the absolutely worst time to brawl. If I have nothing to do, I'll do something stupid and get myself killed. The LRMs let me troll/bait my opponents, and wait for when the organization falls apart and I can really get in there and rip some face off.
If you put this build onto the ON1-M variant you can make it asymmetric. You get the same missile cooldown quirk. Plus you can strip armor from the right arm instead of the torsos... Although it might make more sense to use 2xMRM30s on the ON1-M, so to strap on an LBX10 and take advantage of the double quirk bonus. Come to think of it the ON1-V has really nice quirks for UAC5. So just thinking out loud here. 2xUAC5 and 2xMRM20. Or maybe 2xUAC5 and 1xMRM40!... I think I need to buy an Orion or two!
Thanks for the reply! I'll definitely want to try out the ON1-M variant when I get the C-Bills. I will point out that it's entirely possible on the ON1-V mech to make it asymmetric, but you're right in that the ON1-V configuration doesn't let you strip armor from that other arm. One of the first things I did when I got this mech was try the third one you listed (two UAC5, MRM40). I felt that the firerate of the UAC5 was too fast for brawling. You have nearly 4 seconds that you can turn your side to your enemy with the MRM40, and having to glance back every 1.66 seconds isn't great. I also found myself trying to snipe with the UAC5, and finding that I couldn't beat other snipers who perhaps had some PPC's or something. I also tried UAC/20 and that seemed much better, but ultimately I went back to MRM80. It might just be a skill issue. I'm new to the game, and experience a fair amount of internet lag, which makes it harder for me to hit CT consistently. Thus I prefer splashing 80 damage over my enemy to weapons that require a fair amount of accuracy to be useful. I do at one point want to try some PPCs and see how their long duration works with the long duration of the MRM's.