By accident of timing I ended up with a Colchester Gold card but I feel that I should really have a Chester membership instead. It says 'at least' one visit to various other zoos - are you restricted to one visit?
With a Chester membership you can go to Bristol, Colchester, Dublin, Edinburgh, Fota Wildlife Park, Marwell, Paignton (and Living Coasts) and Twycross as many times as you want. There are just two limited reciprocals, Belfast and Woburn Safari Park, you can only visit those once per year.
I've got a Colchester platinum card and have also used it to go to Chester a handful of times and Twycross several times. In fact at each zoo they barely glanced at it, whereas at Colchester it's always scanned.
However ...... have just looked at Colchester's website to check if, like the Chester card, it gets you into Woburn (it doesn't) and it now states that Colchester cards get you only 1 visit per year to Chester. This must be a recent introduction as I used it there 3 times last year without any problem.
I thought you could only go to another zoo once with the Chester membership?