Both grip and winder add some weight and bulk. To me, that's the only downside.
I find the grip improves handling considerably. The body fits the hand better, allowing secure holding with less finger pressure; the body rests more in your right palm, and you're not consciously squeezing the body to keep it from slipping. Combine it with a wrist strap for fatigue-free one-handed holding: thumb behind wind lever, body/grip nestled in palm, the whole rig stabilized by the strap. I haven't found an RF body yet that didn't handle better with a grip, and I'm trying to figure out how to add a grip to my Canon 7S.
The winder is great for left-eyed shooters, allowing you to concentrate on the subject, without having to push the body away from your face to advance the film. I seldom use the winder for rapid firing, but it stays on the body because of the better handling. Having the Bessa Trigger Winder with built-in grip is kismet. If you are a compulsive focus ring tweaker, the transition from wind to focus can feel awkward until you get used to it. There's more back-and-forth action with the left fingers for sure.
I find a bottom grip improves the winder handling. The bottom grip nestles in your left palm, giving a more natural squeeze action on the trigger. This adds more bulk and weight to the package, but you can remove the winder in less than a minute to get back to basics.
I seldom take mine off, but I'm not sure whether I'd like it as much if I were right eye dominant.
I've never liked or understood hanging a body vertically---it just doesn't work for me. Takes longer to get the camera in my hand, the straps are always in the way.....I've tried, but can't get used to it. I understand some folks like it a lot, so I'm glad the winder gives you the option. The extra lug doesn't get in the way.