Not true in my experience mate I'm in the UK and almost always get magic. DNM stuff is the best because the reputable vendors get their product straight from NL (okay often it's trafficked through Germany first) and then direct to you, no cutting in the middle. This has been confirmed by EC lab tests. The UK gets MDMA that is 90-99% pure. And obviously pills straight from the big crews like Q-Dance are banging and we get those by the tonne.
In fact the big problem we have in the UK with MDMA is that it is too strong and people are taking higher doses than they should because they expect a low quality product (and just because we have a culture of boshing shit, which is fucking stupid).
Here's a pretty in-depth report about changes in MDMA production and purity, also suggesting an increase in MDMA production from China and Canada:
The main source of MehDMA is copycat pills and cut powder. If I had to guess, I'd say meh synths are more likely to come from cheap Chinese sources than our neighbours in the Netherlands.
Anyway, OP, I'd recommend a MAXIMUM of 200mg. Go over that, especially with limited experience, and you will have a harsh comedown for a few weeks. But as others have said, if what you have is truly high quality MDMA, you should roll nicely off 150mg.