I haven't had a good look yet, there are a few new suppliers entering the market now. I have just ordered one to try.
The only thing I would check is the guarantee, the ones I have been using for the last 7 years have been great, and come with a 3 year guarantee (Vsb) not that any of them have gone wrong apart from one faulty timer. Now that can be seen as a benefit over the integral systems...what happens if the timer malfunctions?
I have just ordered this one, and it comes with a 2 year guarantee.
http://www.farmcareuk.com/shop/product/Automatic-Door-Openers/Chicken-Guard-AST-Control-System
I like this one as I can override the timer, particularly useful for ducks, herd them in, press the close button, the timer should kick in the morning. I also know the company and they have always been efficient. I would rather order goods from an established farming company that I have used before.