The hand guards are really not that bad, minor difference. But, if you are really not going to shoot mainly .223 or 5.56 ammo, why go through the expense? If you have to remove the gas tube and change the bolt, it will become a hassle. A Bushmaster AR DI is a perfectly good piece of hardware, so my humble advise is, do not convert it to a Gas Piston rifle. My logic is the following:
1. A Gas piston conversion adds reliability to extensive/ abusive use of the rifle.Even though some members will debate this point!
2. You are trying to have 3 rifles in 1, 22LR, .223, 5.56 DI/ converted to Gas Piston, therefore you are increasing the probability of a problem, which could affect all three choices.
Bottom line, keep it as it is, for the $400 savings on the kit, you can have a lot of fun with 22LR and a very good .223 ammo channel.
When you are ready to have a Gas Piston only rifle, you can use the above listed reasons 1 and 2, to justify buying it.
It's your call, but would you convert your toaster oven to a microwave and use it mainly as a toaster to save electricity over the oven part?