These days with LNAV/VNAV and GPS updating - NDB approaches per se should be a non-issue. At least in the 737-800 they are. Unfortunately, if airlines wont update their equipment with GPS's and modern FMCs capable of RNAV/RNP alerting etc then these basic approaches are pretty dangerous.
An NDB approach is fairly simple itself - however the errors the equipment are prone to make this quite dangerous. No modern aeroplane should be flying close to the ground relying on 1930's navigation technology. There is simply no need for it. (The only reason we have to is because airports and companys wont pay for the safer equipment or have the approaches charted based on different nav aids).
Safety as always comes down to the almighty dollar. Affordable safety isnt it?