I am a big fan of incident meters. One thing that hasn't been mentioned is that a good digital incident flash meter is an excellent tool for learning the ins and outs of metering and exposure. When I purchased my first flash meter in 1989 it helped me improve my metering/exposure skills immensely. (BTW, I still use that tiny Sekonic L-328; a good quality meter can be a long term investment!)
Some meters have memory functions and are capable of showing lighting ratios as well as flash/ambient exposure simultaneously. Stick with meters that are accurate to within 1/10 of a stop. (Yes, 1/10 of a stop does matter even in the Digital Age.)
I prefer thinking of lighting in stops instead of ratios; it's quicker and more intuitive. With a little experience it becomes second-nature. Using an incident flash meter can be faster, more accurate and less expensive than relying on multiple TTL flashes.
Sekinic and Gossen offer excellent small meters that cost between $250-$350 (those prices are from memory so don't quote me!) If you want to use an incident meter to measure distant subjects some models offer add-on spot meter attachments at a reasonable cost. Incident/spot meter combos are large and expensive. Meters with the smaller diffusion domes are slightly less finicky about how you hold the meter toward the light source.