i like the fact that full syphons are fully silent (because the air is removed from the plumbing which is what creates the noise) the thing i dont like about a full syphons is they have more risk (and no matter what layton says  more risk than durso) you are in essence restricting the overflow pipe by ball valve down to the minimum possible size that will allow the syphon to suck water only (and not too big that the water lowers so far that it starts to suck air) so it takes alot less to block the pipe and flood the tank. ok, so you add an overflow cover,... but baby snails can get through overflow combs, baby snails can live in overflows and grow, baby snails turn into big daddy snails that can block pipes  at least with the durso you can go with a large pipe and still maintain a large enough surface area. i run 40mm down, i could stick a snail in the pipe and it wouldnt do anything to the flow, plenty of room in the pipe to spare. so ok, build extra pipes into the syphon overflow for redundancy, but that then indicates a design flaw in the full syphon - having to add a safety factor, compensating for something that may not have been adjusted correctly or because it gets blocked.  
 
ultimately its a trade off of course between complete silence with FS versus slightly noiser durso. there are clear pro's and con's of each. 
 
however i'd really love a combo of both, dead silent like the FS yet safer and lower maintenance like the durso. also something that does not require a ball valve or any need to make adjusments. can it be done? if there is no other easy solution, then i guess full syphon WITH backup pipe as redundancy (which is the only way i could install it without worrying about flooding the hose  ) is the best way for *complete* silence