There are different styles of one wire alternators, some that do not charge below a certain RPM and others that operate at all RPM's. My first one wire alternator was the type that would not charge below 2k RPM, which I installed many years ago when 1 wire alternators were kind of a new thing. At first I did not think it would be an issue, but after having that one for 5 or more years I was happy when it finally wore out and I was able to replace it with the type that charges at all RPM's.
The point is, if you do decide to go the one wire route, be sure to look at the product details carefully and select one that will best fit your application.
A quick search by me found that most of the alternators on the market now will excite at all RPM's.