In both cases, brine metering is by the level of brine in this
tank, which can be adjusted. In both cases, it makes a
saturated solution, so I don't think the brine quantity has altered.

The issue is that the undissolved block salt, tablet salt and granular salt
will all displace a different amount of water when sat in the tank. This
displacement might also be more or less variable. Block salt will displace a
pretty much constant amount of water and provides the best level metering.
Granular salt will be quite variable in the amount of water it displaces.

I'm not saying that it matters particularly critically, but there is a
difference.

Christian.