I bought a Fox40 and used it in a couple of scrimmages. Some of my fellow officials have said that it seems quieter than a traditional F40. Others say it's the same.
I personally find it difficult from a mechanics standpoint. After using a mouth whistle for nearly 30 years, trying to use the electronic signal creates a quandry of what to do with your hands for penalties, signals, etc. For the record - I personally had similar issues with hand whistles.
It is probably just a matter of drilling and practicing with it, but right now, I will be using a mouth whistle for my upcoming scrimmage and for any varsity contests that are still allowed to be played.