They are comparable in terms of volume and pressure and both probably have similar life spans, but if I had it to do all over again, I would more than likely get the EX over the M simply because of timeframe and customer support .
I am on my second bravo which I had connected to a EX Hurricane(20 Psi). It worked great on the older Bravo for 5 years giving me about 90 % capacity. Then I upgraded to the new Bravo and at that time, ordered 2 m-15's and retired the Hurricane which had been in use for over 5 years. The Hurricane was great but I was worried it was going to need to be replaced at some time since I used it for over 5 years even though it was still pumping oxy out faithfully.
I went with 2 M-15's because of price even though I wanted something bigger. It took a long time to get the M-15's - had to nag the vendor and then had vendor get a tude with me when they thought I was bugging them too much. I went with a vendor that I see all the time on LE.
I also see all kinds of posts and issues on LE with this particular vendor/manufacturer not responding to emails, ignoring requests, delays of months in shipping and just general bad customer service and if you get in their face - you're the jerk. Not exactly the foundation for good business practices.
I even recently sent a PM request to that vendor asking about possibly getting a 3rd M-15 ( what can I say - you can't fix stupid - I should have known better). After 3 weeks and no response, my personal opinion is that vendor doesn't deserve my business ever - PERIOD.
300 and 400 dollar machines are great - problem is - EVERYONE and their dog orders them so there is a huge delay and backlog and some vendors cant and don't keep up with their demand but they'll take your money. They also don't want to deal with all of us nags wanting to know where our machines are so they absolutely do NOT respond to inquiries.
I have chosen to take the hurricane out of retirement and hook up to the outer fire of the new Bravo. It never had degraded, still works great! When I think of it, I have a perfectly good unit that will work great on the outer fire so I am going to run it till it dies!
To be honest, as far as I know, the Extreme Oxygen machines have always held up well. In all fairness to the "other guy", I have used the M-15's pretty heavily for almost 2 years now and have had no issue.
The only downfall of the EX machines, is that its hard to find a contact directly, (you most of the time have to go through another vendor although I have occasionally gotten PM's from EX reps).
If you go with 15's , Three machines will work better for you than 2. If your focus is beads, flowers and smaller sculptures, 2 will work just fine. I feel the need for 3 mainly when I am working with bigger marbles or bigger sculptures.
I will say whatever you decide to do, do a lot of research first to make sure the vendor you choose isn't just giving you lip service, (or worse, no service) , can actually deliver when they say they can. You can find machines all over the place out there but if you order from someone that's going to take months to deliver your machines and not respond to inquiries or requests, I ask, is it worth the cheap price, probably not....
Find out how back logged they are.
Enjoy your new system