Well yes the molecule MDMA is MDMA but.. as we all know that molecule can come in a variety of variations and also salts.
Also it is 9/10 knocked up in a Clandestine Lab which aren't exactly playing it by the book so as a result of this can contain many other CNS active compounds..
Choice / Purity of precursor (depending on where its sourced), synthetic routes, size of operation, cleaning techniques, crystallization techniques etc can all make a big influence on the type of "MDMA" you end up with.
In its context is one MDMA dose from LAB X the same buzz as another MDMA dose from LAB Z . ALMOST DEFINITELY NO!!
Is a powder dose better than a pill dose? Depends on your source. There is no other answer. It is only the fool hardy who believe powder is some how safer or purer than pills and the same goes for pills too.
As a user you are 9/10 in the hands of some kind of gangster operation and I can sure has tell you that your health and purity of pill/powder dose is not on the top of their agenda list.
Is powder purer? Well in the sense that it doesn't contain, binder, fleurs, fillers, dyes etc then yes its purer but in the context of is it a purer buzz? who knows?
Yes a test kit to a point can point you in the right direction in terms of what you are taking but does fall short of indicating purity and cannot always detect adulterants particularly trace adulterants.
Those who are more experienced with the test kits can wing it slightly and look at fizz times, smoke, reaction times and over time be able to "read" these results to a point.. but the "get a test kit" that is quoted on here time and time again is not the answer to everything.. and you still need to have your eyes open and never make assumptions.