To start off, both of these supplements are similar in a lot of ways and different in few. Considering they are both central nervous system stimulants you can expect characteristics similar to any other stimulant, Increased heart rate, suppressed appetite, increased basal metabolic rate, also increased concentration and focus.
DMAA otherwise known as 1,3-dimethylamylamine is structurally related to the amphetamine class which commonly includes prescription drugs such as Adderall and Vyvanse, the amphetamine class is also a CNS stimulant, you can expect the same responses of dopamine, serotonin, and norepinephrine.
Most CNS drugs will resemble one or more of the bodies own chemical messengers, for example, cocaine resembles the chemical dopamine, filling dopaminergic receptors therefor creating a sense of confidence and a high. DMAA is not too different, the chemical structure closely resembles epinephrine, otherwise known as adrenaline. Adrenaline as we have all heard is a big part of the "fight or flight" response. When this response is initiated it tells the body to start breaking down protein and fat, also releasing glycogen from stored liver cells. This way the body will be able to either fight or flee, these responses are critical in a time of stress when the body recognizes it is going to have to increase energy and do it fast.
So as far as overall activity of the chemical, according to the Professional Supplements company, they have found 40mg of 1,3-dimethylamylamine to have the effects of 25mg of ephedra.
We all have heard of ephedra but sometimes it's under other common names such as Mahuang, Ma Huang, desert tea, and Mormon tea. Ephedra again is a CNS stimulant, expect the same as you would with DMAA, both of these increase our heart rate, and this is evidence of an increased metabolic rate. Something to be sure of on these, water retention will be low, stimulants impede the bodies ability to retain water, make sure you are drinking enough water while on this. If the body gets too hot, the hypothalamus can shut down, this can cause a heat stroke which has been found to be evident in some cases of stimulant abuse.
To get to the root of these two, since they are in the same class of compounds, it would be hard to differentiate the two, if you believe ephedra to be dangerous, count DMAA just as powerful. The difference in these two is up to debate, and responses will differ from person to person. The FDA is currently looking into DMAA and they will most likely try and get this supplement banned as well.