I have both and the only time I ever used the low range was when curing my BRS pukani, and even then it was only for the first two weeks. Once the levels were low enough I used the ultra low.
Now the low range only reads 0.00 every time I use it. I would suggest the ultra low it will be more useful in the long run. I don't remember exactly, but I believe it reads up to
200ppm. That is the equivalent of 0.2 if your readings are above that you need to lower them anyway and it doesn't really matter exactly what they are.