the only bad thing about safety razors is the time it takes to shave with it
also learning how to shave with it may also be a disadvantage, you have to do several passes- with each pass gradually reducing the stubble, dont go all at it trying to take it all off in one go
the blades are much cheaper - you can get like 100 for £10 which is a 6 year supply for me as i only tend to shave once a week
you can use a variety of different blades with the razor dont need to always go for the same one
derby's
israeli's
merkur's
geather's
gillete's
swede's
wilkinsons
the lists for blades goes on - i prefer israelis, they are sharp but not too sharp and give an amazing shave from the first to last
the futur is the best merkur to have for learning and keeping, dont bother buying loads of different razors you only need 1 decent one - the futur
the vision is crap - lots of reviewers hate it
the HD and 34 and 38's are good too but i reckon the futur is the best for everyone because you can adjust it to suit you personally - i keep mine on 2