I received my new M4 today and I couldn't wait to try it out after dark. I tried out both the HO-M4A and MN61 bulbs as I don't have rechargeables for it yet. The MN61 gave a wider hotspot with less throw while the HO-M4A puts more light into the hotspot. I ended up using the HO-M4A more as it was quite satisfying to shine it across the fields and down along the hydro towers.
I made the mistake of lighting up my hand with the MN61 and had a negative image of my five fingers burned in my retina for a few minutes.
A very satisfying light and I'm thinking I should have skipped a couple of 2-cell Surefires and bought the M4 awhile ago. I'll eventually get it bored for 18650's but for now I'll get a couple of 17670's for it and run a HO-M3T.