Daniel Defense Rails for M4?

I have a bushmaster type M4 carbine and I already ordered a iphone 4 case and MOE stock from magpul. They are on their way so thats 80 bucks out of my budget. Im in high school and have left over christmas money but I have nothing else to spend it on. Should I belly up and spend a good $280? Im ordering from a trusted site because DD is out of stock on their own site. I have seen reviews and feel like I can't go wrong. However, will this work for my M4? "Daniel Defense Gas Piston Omega 7.0 Large Diameter Free Float Tube Handguard Quad Rail AR-15 Carbine Length Aluminum Black". It says large diameter does this mean it won't fit on my stock bushy M4 or will it work? Thanks!