I've had a Beer52 subscription for the best part of a year now. Overall I feel the box is decent value for money but, at the same time, I feel the selection is a bit 'meh' quite often. I opted for the mixed box as opposed to the pale box. The mix box basically guarantees you get 2 dark beers in each case. Personally, that's not really mixed to my values and would prefer a greater range of styles as opposed to predominately pale ales and IPAs which the boxes invariably tend to be heavily focused on.
Each month has a theme which is often country led. So the latest one is Oktoberfest for example but instead of the box being largely fest beers and such, it's a range of beers from current German craft brewers. There was a South African box recently as well as a Polish box. There's been some decent beers, some very nice and some bang average. It's a nice way to try new beers (some of which you wouldn't otherwise get a chance to) but it's definitely geared toward the pale ale/IPA drinker which is a drawback for me. Also, you're never going to get the latest DDH offering from Cloudwater etc and don't be surprised if, when the box is UK focused, you find a few tins/bottles that you could pick up in a local supermarket.
With regard to the Beer52 brewed beers, there was a month recently where pretty much every beer that month had either been brewed by Beer52 or in collaboration with another brewery (it was part of the theme). However, that was a one off I believe. If all there boxes were like this I'd of cancelled by now.