I have tried all iPhone/iPad remotes out there for Kodi and Constellation is no doubt the best. Works flawlessly, fast, and replicates your entire library on your iPhone/iPad for easy and convenient browsing. It is fully customizable and it works even for all sorts of Add-ons!
What I also enjoy is browsing my music collection on Constellation with my TV switched off, so that I am not distracted by the TV screen when enjoying my music.
I have unlocked the full version once to rid of the ads which was well worth it. Highly recommended!