PyroCreationZ

Wow, hobbychems is bloody expensive
I'd never buy there.

I've bought many times from cooperman (and chatted alot with him) and I can only suggest you buy from him.
His chems are very good quality (high grade) and he has one of the best prices in the UK.
The dark pyro is the one you want and when it comes to making flash you'd want the finest mesh possible. I personally have both Indian & German dark (eckart), these are the best ones to use (2-5µ).
Indian is even better as it's usually finer then German dark + slightly cheaper (due to lower labour costs in India)

One important thing I'd like to say is make sure your pot perch is sufficiently milled!
First time I made flash (using German dark) I experienced the same thing. I used a butane torch and it just would not light!
Then I made a new batch but milling the pot perch much longer. Then mix it with German dark (diaper method obviously) and tested again: PHOOF! Instant bright flash with a nice thumping sound

Since it's the first time (?) you're making flash I'd like to suggest to use as many PPE as you can.
When I make flash I ALWAYS use:
- Chemical resistant gloves
- Respirator which stops both fine particles as well as fumes
- Face shield protection
- Anti static wrist wrap
- 100% cotton clothes
- Remove metal from your body (watch, piercings, rings, belt)

But I assume you already knew most/all of these safety rules

Oh one more thing, when testing, never use a normal lighter as your hand is way too close. Sounds obvious but I've seen people do this!
I personally use incense sticks (taped to an even longer stick) which works perfectly. This way your body is far away from any sparks.
Or you could use fuse but I consider it less safe (sparks flying around) then the incense sticks method + I like to use my fuse for projects and less for testing + incense sticks are cheap.
Some comps might be difficult to light with the incense sticks though but in those cases you can use fuse.