R.I.S vs R.A.S
 

I was going to buy a rail for my MP5 A4 and I cant decide if I should get an RAS or RIS rail is there any pros and cons to each?

because I was thinking about gettin this
http://www.airsoftextreme.com/store/...fe747028391bea
but its a GARS

anyways any tips or recommendations would be greatly appreciated

Thanks