even with a ss ring you can still drop the chain, although you should be using a proper ss ring you can still get a chain guide if you like
but yeah as said above all chain guides are not the same, and as said above dif mounting styles tooth capacity, single vs dual ring ect, but i imagine your question was more of a "why should i drop $100+ on an e-thirteen when i can get the blackspire or truvativ guides for $25" Well I'm not and expert but i've heard that noise is one issue, as well as reliability and general build quality ect ect,
I can tell you this, i jut got an e13 DSS and seems to be pretty awesome (btw e13 has this new line of less expensive guides made of stamped steel instead of alloy) I cand fathom my chain dropping now, and it didn't add any noticable noise as its quiter than the chain moving through my rear derail