@Bob Hi - regarding the P9 unit….how strong is the internal coil. Is it strong enough to treat hip osteoarthritis? In terms of strength, how does it compare to stacking the coils using the A9? Thanks!
The internal coil on the P9 is a bit stronger than a stacked coil configuration on the A9. This is because the internal coils have about half of the electrical contact resistance of coils at the audio connector, and the internal P9 coils also do not have the wire lead resistance of A9 coils. And finally, the internal coils are a double-coil stack, but without the rubber insulation material around each coil. All taken together, I would say the internal P9 coils are 15% to maybe 20% more intensity than stacked A9 coils.
I designed the P9 as a device that has the features and performance that I would like for my personal use, so I really like the P9 a lot. I will probably retire my old A9s and M1s and switch over to mostly using P9s. The only negative about the P9 is that they take me about twice as long to build as an M1, and the total cost for components is higher than an M1. So it will end up costing more than an M1.
I just started making P9s in larger batches (12 at a time), so we have started selling them in quantity, enough for any of our customers who want them.
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Cool, that sounds good.
For “single spot” applications the P9 seems a good device, since there are no extra cables which are always to long or to short and no coils that have to be strapped in place in addition to the M1 
@Bob : Do you have a “rough guestimate” how much more operation time (in percent) a generic Li-9V block adds in comparison to the “average” M1-camcorder-batteries?
yes, I did some 9V battery life tests two weeks ago.
Results: running the same pulse protocol at the same intensity, the P9 lasts almost twice as long using 9V Li-Po USB rechargeable batteries than an M1 using a 3.7 V camcorder battery.
NOTE: it is better to use “honest” 650-1000 mAh capacity Li-Po 9V USB-Rechargeable batteries rather than the fraudulently labeled “1300” mAh batteries, which are really more like 300-400 mAh capacity.
My own experience with P9 (with native coil - no wires) with these batteries https://www.amazon.com/dp/B00HV4KFSA is indeed double the time as the M1 with the wired coil. I do lose approx 15% length of time when I use wired coil on my P9 versus P9 without wired coil