From engineering experience on four blade systems I would recommend the Chadwick Helmuth 8500C+, Its easy to use and you can add all the goodies you want, from basic blade track and balance through to a full 12 sensor airframe vibration analysis which can help pre empt component failure. If its easy to use then you will save money on labour costs - I have seen some amazing things done with this system.
In saying that I can't say I've used it on elastomeric heads........