Here are some (very fluid) generalizations that might help you choose which class is for you.

RMT:
Based on 17 movements (plus others) in procedure formats — or done alone.
Began just 13-ish years ago; introduced 10 years ago in US.  World-wide now; I don’t know country/language count.
Maximum of 10-15 minutes a day.
Only done on the floor
Tends more towards a 1:1 situation, although we do have classes for preschool/early childhood teachers to implement with large groups.  I’ve gotten entire classrooms doing exercises at one time.
Being able to touch the person is necessary for some exercises.
More aimed at medical professionals, though everybody likes and uses it.  I think.  Maybe that’s not a fair generalized statement.
Results tend to be stronger and more dramatic.
More structured towards symptom-list (reminds me, an RN, of syndromes):  Does this child have not just bad, but atrocious and chaotic, handwriting?  How about can’t organize worth beans, always losing homework and can’t find neatness?  Nor pay attention?  Overly tight pencil grip?  W-sit?  Okay, not w-sitting but sits with one (or both) feet anchored under the other leg?  or hooks feet on chair legs?  Very slow copier, terrible memorizer?  Does better if he stands at a desk in the back of the room to write, or slouches so he can keep legs entirely straight?  It’s likely ALL due to ONE unintegrated reflex.
Absolutely, positively need to be in a hands-on class.  I’ve had considerable difficulty getting people to un-learn techniques learned informally from someone who’s been through a class, and tried to teach a colleague.

Brain Gym:
Based on 26 movements in procedure formats – or done alone.
The 40+ years, in 80 countries, 50-ish languages
Done whenever, however.  Two are best on the floor, but adaptable otherwise.  In formal situations as well as at stop lights.
Easier to teach to entire classrooms at once; movements are more easily mastered.
More aimed at teachers/parents, though everybody likes and uses it.  I think.  Maybe that’s not a fair generalized statement.
Results can be quite dramatic.  Wildly appreciated by all.
More structured towards function:  Do you want to write better?  Listen better?  Organize?  Focus?  Move in the midline better?
Easier to do for more than 15 minutes a day if the person prefers; easier for person to implement later on (students frequently do, on their own.)
Marvelous at addressing ATNR, even indirectly and right-left brain integration/corpus callosum strengthening.  (Brain Gym doesn’t claim this, I’ve observed it.)
PTs and OTs frequently mention how much their clients like and request the movements.  Teachers likewise talk about their student’s independently initiated use.

BOTH BRAIN GYM AND RMTi:
Widely applicable to just about any challenges in life: anxiety, memory, public speaking, posture, attention, sensory processing, balance….you name it, it works.
Are highly adaptable to whomever you’re working with, with whatever ability level (including comatose patients). Infants to elderly.
Exercises are incredibly relaxing, or energizing –and sometimes both at the same time!
Are widely and enthusiastically accepted/frequently requested by widely diverse populations
Easily incorporated in 2 minute or more segments into existing sessions
Easily taught to clients/families (who also love them and benefit greatly from continued practice at home)
Strongly potentiate one another, interweaving exercises and effects.
Help with just about anything/everything people do.  Mental health, posture, public speaking, organizing, communication, falling asleep
Surprisingly helpful to the person learning these techniques (i.e., therapists, chiropractors, doctors, nurses, parents, etc.)
*The basics are taught in three very packed days
*There are some minimal things (charts, cards etc) you CAN buy to supplement, but truly — both stand freely without any further expenditure
*Both are open to and learnable by any adult
*The implementation of these disciplines are as much or more art than science
*You are strongly advised to take the courses twice, as there’s a lot of somatic learning and everybody is surprised at how much they learn even the secondtime through.  With both programs, people repeating that course only pay half-price, even if you take it from a different teacher (which is advisable.)
I get rave reviews from OTs, PTs, SLTs, sped teachers and parents about both Brain Gym and RMT.  Teachers of all stripes, mental health professionals, parents are among those who swear it has dramatically changed their lives — and those they work with — for the better.
Happiest definitely are those who have taken both.