A couple friends have PWS muzzle brakes on an LR308 and AR15. They compensate well. When you look at muzzle brake's there are some things you need to weigh:
a) the obvious is the brake's contribution to shootibility
b) the adaptability of the brake to other weapon components such as suppressors
c) how much trash the brake throws back and its effect on bystanders.
On handguards, I'm waiting on Midwest or someone else to bring a 15" key mod to market. According to a post by MI on ar15.com, this will occur very soon. Midwest is already taking pre-orders on the shorter 12" key mod. They posted a demo photo of the handguard mounted on an m&p 10 on ar15.com as well.