Certainly helps you this year, assuming there aren't comparable players to Hertl available.
So assuming you don't keep Hertl you will be going from Hall to Ehlers as a keeper. I still have Hall slightly above Ehlers in terms of keeper value but if Ehlers keeps producing like he is right now then maybe the gap isn't there, especially with Ehlers being a bit younger.
Seems like a decent offer, but the questions to ask is if you are okay with the change to your keepers and is it worth it to get Hertl vs just keeping Hall and adding a poor man's Hertl off the free agent pile.