There are a number of unique plate designs (e.g. the Freedom plate) that are truly exciting. But, generally, you are right far more similarities among backplates than differences. Most SS BPs fall into the 5-6 lb weight range, but with a few exceptions. Most plates (SS and AL) fall into a particular size range (approximately 10.5 W x 15.5 L), but there are some made for taller / shorter people. Backplates may differ in the configuration of the holes drilled in the plate NOT the distance between the centerline bolt holes (11 OC is the standard), but in the number of sets of centerline holes, in whether there are slots cut for tank cam bands so you can attach a single tank without a STA, in the location and number of holes drilled around the edges to allow attachment of equipment, in whether there are one or two slots cut for attachment of a crotch strap (and, if there is a single slot, whether it is a 1 or 2 slot). You will see comments about the quality the specific SS used and whether it is more or less resistant to oxidation, about how clean the edges are (are there burrs that may snag webbing or exposure suits, or are the holes / slots clean), which Lynne mentioned. You can 'dress' an AL plate, or even add holes, whereas doing so with a SS plate requires equipment, and skill, that the ordinary user may not have. I have three standard size SS backplates, including one homemade, and like them all but the homemade definitely has rougher slot edges than the others. I have no personal experience with the Salvo plate, so hopefully others can comments specifically on that brand. The good news is, that having local service is probably NOT a critical factor in BP selection.