All of the ones on the market are good.
The PACT Club Timer III (and the Mark IV timer/chrono...if you need to chrono stuff) are great.
The Competition Electronics Pocket Pro line is great (the Pocket Pro II has been discontinued, but they are still out there for sale).
The CED 7000 line has loyal followers...
Bottom line:
Invest in a genuine shot timer and don't bother using a phone app.