I have a Dryfire system and have been using it to practice doubles which I haven't shot for ten years due to going to a release trigger in my Alfermann. After converting it to release and shooting it for a while I reached the point with the almost no trigger movement to release my Alfermann, I would not move my finger enough to set the trigger on my Beretta for the second shot. I blamed the Beretta trigger for this and finally traded for a Kolar and had the same problem. And I bought the Dryfire unit to let me practice shooting doubles at home where I could just concentrate on the trigger set without the frustration of screwing up on the range and creating other problems.
The Dryfire requires you to enter all the vital info about your and your shells, such as POI, choke, and shell speed and pellet size It provides you with a lot of feedback about what your doing. The one drawback I've found is there's no recoil. The first time you go the range and shoot, you think your gun is going to jump right out of your hands for the first 5 - 10 shots. It takes a few times going to the range and this goes away.
Big advantage is you save the cost of a box of shells and a round of targets. Plus you don't have to bundle up to shoot. You can shoot in a tee shirt.
I have had a Dryfire unit for 4 years and I find it invaluable. Once you enter the data, you simply start your computer and you are ready to shoot. The unit tells you how far ahead/behind or high/low your shot actually was for singles and handicap (my unit doesn't have doubles). You can even set it to throw one type of target to practice your weaknesses.
The version we have is a US model. One important asset to Dry Fire is Dry Fire Bob! Bob knows the system inside out and will spend the necessary time to insure you have a good working system. IMHO the Dry Fire is worth the money but only if you use it. My wife spends a lot of time with it and has had the same recoil experience. She will usually shoot a practice round prior to shooting for score. There was a unit on here for sale a while back. Jake
Since I posted, I thought about how I shifted my free time from trap to bicycling. Therefore, I would sell my Single Head Dryfire system. I have a unit that Bob replaced with a new one in March of 2012 with version 3.1.3 software. I have the acoustic trigger (release). I also have the canvas and the Styrofoam trap house. I also have the unit mounted on a tripod and connected to an old laptop that I just use for the DryFire.
This all purchased new today is $ 1,470 not counting the laptop and the tripod. I am in SE Wisconsin. Anyone interested in purchasing?