nature detectives, wildlife watch, RSPB etc - any recommendations?

[nearlytoolate]

Looking into getting ds2 (aged 6) some kind of subscription to a wildlife magazine/activity club. Options seem to be RSPB Wildlife explorers; Wildlife watch (linked to local wildlife trusts); or nature detectives (run by woodland trust).
Does anyone have any experience of these and can recommend them? Or have found them a waste of time/money?
Hard to know which might be the best!

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I can see I'll have to try this one again in September...

My kids had a free membership to Natures Detectives & I thought it was great. They send lots of fun, seasonal activities & we couldn't even keep up, so I think it's good value for money & would have been happy to pay for it. There's a Tesco clubcard deal so I might join again when we finish the activities we didn't get to do.