None of the iOS meditation timers on the App Store are worth bothering with.
iOS has got built in timer functionality in the stock iOS Clock app (Instructions for setting timers can be found here). However, the default timer sounds are unpleasant (aversion!) to hear when returning from meditation.
The best meditation timer app I have used on Android is the open source Bodhi Timer made by the Venerable Yuttadhammo. This Android app contains a number of free timer sounds in Vorbis format here.
These sounds can be converted for use with the built in timer functionality of the iOS Clock app.
Convert the Vorbis files to "m4r":
$ cd BodhiTimer/app/src/main/res/raw
$ for i in *.ogg; do ffmpeg -i "$i" -c:a aac -f mp4 -b:a 128k -ac 1 -filter:a "volume=0.1" "$(basename "$i" .ogg).m4r"; done
Now connect your iPhone to your Mac and go to the General tab of the device in Finder. Drag and drop the newly created .m4r files anywhere inside the General tab and they will immediately be transferred.
Create a timer and set the When Timer Ends to your newly transferred ringtone e.g. bell.
Sadhu! Sadhu! Sadhu!