"The Combro is an excellent little piece of kit, fine for PCP's but not so good on springers due to the recoil. They can be used indoors and they're nice and compact. I don't use it now as the Prochrono does virtually everything I need." (Quote)

I have been using a Combro exclusively on springers for about five years now, with absolutely no problems. It is only held on with a rubber band, which adequately absorbs the recoil. Absolutely fine for keeping legal, comparing pellets etc, but not quite the answer if you need downrange readings.