Not everyone needs a click track, but even the best of musicians can struggle at slower tempos on a Tuesday morning in an unfamiliar environment with headphones strapped on. If the band is tight, I shy away from smearing headphones with nasty bleeping tempo reminders. Pro Metronome is an easy to use yet advanced metronome app for iOS and Android, with all the standard functionality you might expect (tap tempo, click sounds, etc.) plus advanced features such as customizable time signatures, horizontal screen support, programmable playlists, Inter-App audio support, Airplay compatibility (for mirroring your iPhone display on a large screen or projector), a practice timer, and multiple beat display modes. The beat display modes are Pro Metronome's best features. You can configure unique visual cues like screen flashes on all beats, or a bar count that triggers your phone's flash every measure. The GUI is elegantly simple and easy to see in different lighting scenarios.
During a recent tracking session, the drummer had his phone simply propped up horizontally on a music stand, and with visual metronome cues only was able to fluidly guide his band through tight performances while maintaining a natural rhythm and feel that never came across as mechanical or rigid. This method helped to keep the other musician's attention where it should naturally be, without an unnatural electronically-generated blip constantly flying around in their ears. In some instances, the band stopped following the click altogether after only establishing the tempo at the beginning of the song.
My favorite feature of this app is simply that you don't need an audio cue due to all of the useful beat display options – no noise means no headphone bleed. I found most performance results to be tempo cohesive enough for on the fly editing. Note: EUMLabs claims a beat accuracy within 20 microseconds – not bad for a phone. Pro Metronome may not be the right tool for every situation, but before sessions, I recommend suggesting this app to clients that struggle with tempo. It's a good training tool for pre-tracking practice sessions but can be equally efficient in the studio if the fit is right for the project. New features, like a tone generator and tuner, are typically added with every update. I paid the $3.99 for advanced beat display modes, but trial/fee mode still offers a lot of features, and there's never any ads!