there is no way fmcb could "break" a ps2,since its just a bunch of data(so to speak, and i dont mean it in an offensive way) in the memory card. How did your friend says fmcb "broke" his ps2? Its not that fmcb and ESR work worse on slims(i've tested it on a slim, works fine), i guess its more of a laser issue. Bottom line, something else broke your "friend's" ps2, nit fmcb.
V7 ps2, flip top, 2x 8MB sony memcards, FMCB 1.8b, ESR r9b, Cogswap, Hdloader0.8c, 250 gig Western Digital, poorly modded(but functional) network adapter