I used a digital one from a kitchen shop for my IR. Don't bother with an analogue one - if it is dark it can be hard to read the minute hand (well I found it hard anyway) and under pressure it can be hard to see if it is two minutes or three.......
I think I paid £5.99 for it and it does all the things that the Transair one does for £20 less. If it has a clip, it will be useful for clipping to your kneeboard.
Hufty