I was using the D'Addario Planet Waves NS-Micro tuner, and after getting a half-dozen of them and keeping them on various ukes, I realized that the constant battery changing was costing me a small fortune. After about 30 days use, the batteries (in everything) in my house seem to go flat. Now they are all in a cigar box in my drawer, unused.
see here:
https://www.amazon.com/DAddario-NS-Micro-Clip-On-Tuner/dp/B005FKF1PY
I grabbed one of the Reverb tuners when they went on sale for $1 with free shipping. It works well enough. Next time they went on sale, I bought myself a 5-pack as 'backups', none of which have even been opened yet and are in the drawer for when the first one I bought finally dies. It is still going strong 2 yrs later. Battery lasts a long while too, which is nice. see here:
https://reverb.com/item/204704-reverb-clip-on-tuner
For an app, I like and used instuner on iOS. It has several different modes, including 2 'strobe tuner' modes, and was free when I bought it. see here:
http://eumlab.com/instuner/
One of the things I like about instuner is that it shows the OCTAVE of the note you are in, which is very handy for string changes so you done overtune to an octave too high and pop a string from excessive tension.
Would that I could, I'd like to get the TC Electronic PolyTune clip-on ($49) which has a strobe mode, or the Peterson Clip-on Strobe Tuner ($79) but that's an awful lot for me to spend for
precision that I can get from a free app.
Maybe if I win the lottery and after ALL debts are paid, I can 'splurge' on such a fancy tuner - LOL