This sort of question is hugely dependent upon what sort of printing you do and what your expectations are.

If you are a shoot lots and knock out a print or two, then move on never to return - then no you probably don't need a fancy timer, counting will probably (just about) do

If you are a high end printer doing fine art or exhibition prints or similar then yes you will NEED one

Personally, I was more than a little skeptical about would an RH StopClock Pro be good value for money when my friends advised me to get one

Having bough one and used it a few times, I would say yes they are great value for money - expensive, yes but definitely worth it

However, YMMV

Hint - have a look on e-bay for second hand RH equipment to see whether existing owners think their stuff was good value for money - about as common are common as bags of rocking horse manure