Wipey96 if your going to stay around, please add your location to your profile so it shows under your name, you should also post an intro thread in the Welcome area.
You should have posted here first asking where and what to buy instead of buying and asking was this a good purchase. Then you would have got some safer recomended sites to buy from.
It remains to be seen if you got scammed. There are even more expensive high quality pen type lasers, the cheap less than $10 ones from China are always a gamble, the one I bought lasted only 10 days. The 4B thing is disturbing but it could just be a mistake, it should be 3B, also I have never heard of megalaseruk.com, so it is not a well known site here, it could just be new. Let us know if you get what you paid for and if you are satisfied with it. At 50mW it should have a visible beam in dim light or in the dark, it may burn black plastic or pop a black baloon but 50mW is borderline for that, pens like that aren't focusable so not as good for that anyway. Hopefully you get what you paid for.
Edit: I am mistaken, they aren't new, there are many threads on them going back a few years, it looks like mixed reviews, you will at least get your laser. Let us know how it turns out.