I use it on new tanks to make sure there is no ammonia before putting in fish. Definitely worth it IMO cuz I always put a well established sponge or bio media in when starting a new tank and I want to be positive that there will be enough so that a fish doesn't have to go through the stress of a mini cycle. Only once has it read that there was ammonia and I'm glad because I was about to put a mormyrid in there which are extremely sensitive to any traces of ammonia.
I keep one of these in each of my tanks. I still test the water params weekly but it's a little reassurance that I like to have. A quick glance and I feel better. For the money I say the peace of mind is worth it.
I normally would not buy products like the Seachem Ammonia alert device but picked up the Ammonia and PH combo. The Ammonia alert has a expiration date of 1 yr. and after the PH alert has exhausted there is a replacement alert tab in the package. Please read the instructions thoroughly prior to use or you will be confused.
This was a great vid that is very helpful if anyone was interested in buying this product.