I take it your looking at the ICS ones? If so they are good solid guns the only problem is accessories and magazines.
Yea, really like the look of the ics 552 but noticed the 551 has an updated rail system/longer barrel. You got one/used one??
Thats the MRS version with the quad rail, both the 551 and 552 come in that version. I have a Sig 552.