If you are tall, finding a monopod that will work well with an SLR might be difficult. Mine only extends to about 5', but my main use is with Mamiya C twin-lens cameras, or my MPP Technical. Both of those are heavy to hand-hold for a long time. I have a Benbo ball head on mine so that I can lean into the monopod and keep the camera level. I got mine when I was doing a lot of hiking and cycling and carrying a tripod was difficult.
Used with care a monopod should give you an extra two stops slower shutter speed (subject and photographer permitting), but that is not my main reason for using one.
I have a Manfrotto and use it a whole lot. It is not a tripod substitute, but can get me 2-3 extra stops beyond what I can hand hold. I'm 5' 6" so it's high enough for me, plus I usually add a swivel head from a light stand so I can tilt the camera up or down without having to lean the monopod.
I, too, use a monopod for marginal lighting, more mobile than a tripod, better than hand holding.
Mine is a Tiltall - very simple and well built, a popular brand before Manfrotto became as popular in the market.