ringlights are funny things.
When used alone, they provide the tell tale shadow around the entire subjet, if there is a background close. If not then it provides even lighting with a darkening of the skin that is curving away from the lens. It is a nice effect for either the main light, or fill.
Ringlights if used for the main light can be very harsh on models faces, so you need to have near perfect skin ( the models that is ). It is unforgiving for models who have bag lines under their eyes. Unless you want to spend hours photoshopping.
The profoto ring is nice- very nice. I would also recommend the optional soft reflector for it ( 250.00 ).
In all it comes down to style, what you are shooting, and how much cash you have laying around. A pro ring is around 700, and to get the most of it, either a 1200 ws or 2400 ws pack should be used, although- this is the key, you are not supposed to put more than 9600 total ws thru it per minute. Typically with a 10 foot shooting distanc, you will turning the power pack way down, and still good aperatures ( f5.6-11 asa 100 depending on the pack ).
On full power at 10 feet with 2400 ws you can shoot near f32. That is enough to turn mid day light into near darkness if you have a good sky. Models either dont mind it, or hate it ( it leaves circluar white spots in your vision after each shot ).
One thing I hated about it. If you move closer or further from the subjet, you need to re meter each time. So, it becomes almost necessary to use zooms for fine adjustments in framing. then the distance can be the same, and you can re frame on the fly. This doesnt lead for the best shooting ( my opinion and techniques, but then again, re metering doesnt take long). After time, you will be able to guess the exposure change ( print film and digital ), but with slide film, re metering is necessary.
One thing you can do is get a Sunpak Dx12r battery powered ring. Its about 229 or so from B&H. And an adaptor for 20 or so. Do not attempt to get the ttl adaptor- unless your camera is specifically listed.
Hope that helps.
Profoto ring image
Profoto Ring also
Ringlight as fill. Main was a strip dome to right, and large reflector in front on the floor.
Chip