Prussic acid is not a danger with Pearl Millet, but it is with Sorghum/Sudan. I've planted many acres with Pearl as a cover crop, usually after pushing up old brush or reclaiming an old pasture. It grows VERY fast. You can usually graze it a month after planting. Horses and cattle love it and it has a decent protein level. Fares well in drought but will not do well in poorly drained soils. Also remember it is an annual. As soon as it begins to cool off in the fall, the millet will brown up and go away. If you don't graze it too heavily, you could also enjoy some excellent dove hunts in the fall.
I never had much luck shooting doves over Pearl Millet, but it is a good cover crop for "plowdown" and grows like weed during a drought. I am considering planting some pearl millet for hay, but it might take too long to dry with being cut by a sickle mower.
Shiner Bock -- the longer dry time is the problem I've had with similar forages when cut for hay (Haygrazer, Sudan, etc). But they sure do grow awfully fast under the right conditions and the cows love the hay. A crimper probably saves you a day. I know from experience how really disheartening it can be to watch the bermuda guys cut one day and bale the next, while waiting for my Haygrazer, etc. to dry --- especially when you get in one of the periods of frequent summer showers. Not to mention that the hay meadow takes much longer to dry out if you get a rain on the standing forage, as compared to bermuda.
Like DR Cattle, I have also had good dove hunts over that type of hay field. You might consider leaving some strips of millet, Haygrazer, etc. to head out in late summer and then shred them a few days before dove season starts.
We planted pearl millet a few years ago along with a neighbor. We had a hard time getting it to dry also, and he claims he had a high nitrate level in his. He baled later than we did. After a slight frost , but we also planted late. It does grow fast, but winter rye is the fastest growing stuff I have seen, just an option!