Stephen, the question in your original post seems to have been ignored!
ie, "What are the pros & cons of each?"
I guess this is to be expected, as the "right or wrong"ness attitude will often rear it's ugly head when Our Beloved Forum sprouts debates such as this!
Some genres of music and/or playing styles will involve different techniques which will naturally tend to favour one bar or the other, however in reality it's personal preferance that determines bar choice.
To your question:
Any cons associated with either type of bar are able to be overcome by adaptation of technique.
( Please note that the following is all IMHO )
Vibrato: This is not affected by bar-type, though the diameter of a bullet-bar or radius of the playing surface of a grooved bar have an effect on the "rolling vibrato" technique.
Hammer-ons: How can bar-type affect this? Maybe in this case the bullet-bar is at a disadvantage, but only if you don't tailor your grip or choice of diameter to suit.
Pull-offs: Some use the edge of a shaped bar to "pluck" the string, but a bullet-bar is just as effective for pull-offs by employing a different technique.
Open Strings: A bullet-bar will slide more easily onto or off an open string whilst remaining in contact with the lower strings, as there's no "edge" to catch. A "Stevens"style bar requires a different technique to avoid involuntary pull-offs or snagging.
Single-strings: Either style is equally able to play cleanly on a single string without contacting adjacent strings. The same applies to double-stops.
"In & out" movement with a grooved bar requires muting of unwanted strings.
Slants: Many find that slants come easier with a bullet-bar. A grooved bar is only less suitable for slants if you rigidly apply the incorrect technique.
Slightly arching the index-finger to provide the fingertip as a fulcrum for bar rotation can be accomplished in a split-second without requiring any unnecessary rotation of the hand.
Some complex slants though are impossible without a rounded nose unless you employ a nifty string-pull whilst slanting.(:whoa:)
Lifting or not lifting the bar: Some say that lifting the bar is an
absolute NO-NO... IMHO that it their HO which applies to specific genres of music, and should be taken as such. For some genres lifting the bar is
essential.
Bar choice is largely down to personal preference and imVHo the factors involved are subjective, through adaptive techniques the cons of each can be overcome, as proved by the highly accomplished players out there who use the "wrong" bar.
ie: Dobro-players using a bullet for bluegrass & Stevens-bar-users playing traditional Hawaiian music with slants aplenty.
To each their own, I say!
It's unfortunate that there
seems to be a tendancy for advocates of bullet-bars to come across as dogmatic!
For this reason alone I'd say that
you must avoid bullet-bars entirely as they clearly induce some kind of delusional and/or phobic behaviour which manifests as the unpleasant symptoms of hatred and dogma.*
I've yet to find a quote of any grooved-bar user which goes anything like:
"The bullet bar is an absolute piece of junk", though one could just as easily come up with a similar diatribe bemoaning the shortcomings of bullet-bars when faced with the immovable conviction of personal opinion!
*Note to those without UKSOH:
I'm JOKING.
Seriously though, try both & use what you like.