These monitors y'all have seem to be much more accurate than the push pen device. I even gave thought towards getting one but decided instead to buy two new 5 gallon tanks with mechanical tank level from Costco, $24.97 ea. With the auto switching device on the regulator and having a pretty good idea as to when to look at the tank gauges which is VERY infrequently I might add, I'm good and don't have to worry about replacing batteries and the like.
Those devices are pretty cool though especially with the ability to check tank levels while residing inside the RV by looking at your smart phone.