I have a Prochrono and a Combro, a mate has recently bought a Skan and I have another mate who has the Chrony.
The Prochrono is excellent and I did plenty of research before I got it. It performs well in all lights, it can be used with a laptop and it's easy to use. On the downside it only shows fps not ft/lbs, it can't be used with an android device and you need an extra lighting kit to use it indoors.
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.
My mate bought a Alpha Chrony and lighting kit last year and it very rarely gives a reading, it's really light sensitive even with the lighting kit. It cost just over £150 in all and he doesn't bother using it now, waste of money. From what I've seen I wouldn't bother and look elsewhere than this make.
As most know the Skan is a great piece of kit, another mate has just got one and tests his guns in his shed with it. It shows both FPS and ft/lbs and can easily be interfaced with a computer, it's easy to use and comes with comprehensive instructions that anyone can follow. The Skan has recommendations that it can only be used indoors and it's expensive, it also needs to be used on a firm rest that allows good alignment between the muzzle and scope.
With that all said if I was going to get another chronograph I'd go for the Caldwell Ballistic as it has everything I need. It can be used indoors and outdoors as it comes with a lighting option, it's not light fussy, it's easily interfaced wirelessly with an iPad or iPod, it gives comprehensive readings and the menus look easy to use. However, if you want the all singing, all dancing options the price might put you off and the Prochrono may well be your best option.
Good luck with your choice.