Hi (John really).
As with any cutting tool you really need a bevel to control the cut, especially if it is one you use single handed as when parting off. On these thin parting tools you normally have a 45deg bevel about 3 - 4mm long which is the one you use for control not the big bevel.
Used without a bevel they can be a bit vicious, and be hard to control, but some people prefer them that way. Personally I use the bevel.