Would they thump or we talkin cheap stuff

Was shoppin for subs and the guy prity much had me talked into these. Havent realy decided if its enough sound tho, talking about a prity seriose system. I mean the guy gave it a little in the store but not enough to get a realy good idea. so if anybody has any experienc with these subs if you could give me some feed back that would be great. thier 12" Thunder 5500 or you can go to the link below. thanks

http://www.circuitcity.com/ssm/MTX-Dual-12-Subwoofer-Enclosure-Package-SLHT5512X2D-/sem/rpsm/oid/118651/rpem/ccd/productDetail.do