That's an inspiring story, thanks! I'm on the road but will specifically try different reflectors when I return. I have been using metal foil tape which certainly seems reflective enough, but who knows. Thanks again!
You didn't mention if you needed a handheld or mounted solution however one brand that has worked great for use at work is Shimpo. We have used older variants of the DT-207 series at work for years:
http://shimpoinstruments.com/tachometers/dt-205lr_-_dt-207lr. These are built like tanks and the only failures we have had are leaking batteries creating grief. They have a whole series of tachs so you have choices beyond that.
At work we make use of permanently installed tachs that use a laser head combined with a DIN rail module. Unfortunately I'm not at work and can't remember the brand name.
As Tautech pointed out there is a massive difference in the quality of retro reflective tape which causes us problems with not only tach readings but in the use of various optical sensors. As such you may have to experiment with the various reflective tapes on the market. Sometimes you are better off with a retro reflector but those seldom are usable on rotating shafts.
As for brands of reflective tapes, we have many around the shop so I can't tell you off the top of my head which have proven to work well. Sadly some tapes are not much better than black flocking, seriously!!!! I can also confirm that what is supplied with a meter isn't always the best retro reflective material out there.
The other issue you might run into is lack of contrast between the reflection off the target and the shaft itself. We have had this issue with stainless steel and have made use of black tape to mask off everything on the shaft but the retro reflective target. Fortunately this is on a low speed, small diameter shafts so we don't have balance issues. On high speed devices you may have to take precautions with respect to balance.
One other trick that I've had work for me is the no reflective tape method that makes use of a setscrew hole or other hole that might be on the shaft or component on the shaft. Instead of a reflection you rely upon the lack of a reflection. In terms of electronics it would be like looking at the portion of a square wave that goes to zero. You would likely need a laser baser tach for this and one that would understand what amounts to an upside down wave form. The no tape method can save you some grief. Other no tape approaches include Sharpy markers, flat black paints, and even white out "ink".
By the way White Out Ink should be in every bodies tool box. There are all sorts of uses for the material that have nothing to do with typing. That would be a thread all on its own.