I did NAET for several years and it can be effective. However, if you have a root cause for your allergies/asthma, then unless you get the root cause addressed many of the treatments will not be effective long term. For me, the root cause was mold exposure and until I got out of a water damaged house (small amount of visible mold), I would feel great for 24 hours after a NAET treatment and then go back to feeling bad again. NAET was extremely effective for me in treating an allergy to a medication that was an absolute necessity to remove the toxins I had been exposed to in the moldy house. I think NAET can often be extremely effective for environmental reactions - i.e., airborne allergies. However, unto itself it generally cannot result in your body being able to detoxify environmental toxins such as mercury. I felt terrible after a NAET treatment for mercury because I was not taking anything to bind with the mercury and remove it.
I also had a NAET treatment for my reaction to my house (I brought in dust samples in a baby food jar) and that did really help for a while. BUT, I decided to clear out some old stuff and was exposed to too much still for my immune system to handle.
I also strongly believe that things like gluten/wheat intolerance cannot be treated with NAET and that there are some foods for which your body does not have a tolerance in general and even if you get treated, likely you may have problems with that food later on in particular in any quantity. For example, I was treated for an egg allergy, but still have problems with eggs. However, I can sometimes have egg in a baked product. In my experience, the food allergies often go along with issues with toxins and it's often the toxins that disrupt the immune system thus causing these reactions to allergens.
I definitely think it's worth a try for anyone with allergies, just don't expect miracles - it also takes time (for each treatment and for treating all the allergens) and not all insurance will pay for it. So, you really have to figure out if the benefits outweigh the cost, which is a very individual thing. One of the most difficult things with treatment for the airborne allergens is that for NAET to be most effective, you must avoid the offending substance for 24 hours - tough to do when you have to breath. You likely will need to wear a mask.