Sorry Guys unless you've just started you've got experience. The shop is out to make money as is every shop. Don't buy from them if you can get it cheaper elsewhere. But if they are the cheapest buy it.
Read their description fully be sure what is in the packet simple
Do your homework before you buy it read up on the item asked others what it is like
Cars never do the MPG that the makers say. There is a bloody good chance that the AEG won't be the fps they say
You know as well as me that there are many different factors to be taken into account
Age and condition of spring battery and what chronograph they are using
If the price is good use them
If not don't simple
You can see by most of there stuff it's aimed at the lower end of the market ( you can tell that by the videos and by the comments left by kids on their page )
I have used them and not had a problem they had something others didn't and I wanted it I got it with no issues
Read reviews on all shops they all have people bad mouthing them if you don't like it don't use them