I'd still like a temperature sensor with a E61 group.. something located near the screen area. The PID is in the brew boiler and there are lots of influences between that and the E61 group. If your group is cold, then it will cool the brew water much.. if it is hot (you've just done a flush after 1 hour on). It will obviously not cool the brew water. Thus, all the PIDs have an offset built in, but with an E61 it cannot be exact as these influencers change with time, work flow, environment. You also have no idea when your E61 group head is heated sufficiently (from off). Generally it takes about 45 minutes, but if you are in a hurry, you don't know where the group temp sits at, say, 30 minutes. All you know is the PID reading from the brew boiler.
Saturated groups have much smaller groups and the brew boiler is in the group so there is much less of an influence by external influences.
You may buy an E61 DB thinking you control the brew water exactly, but the manufacturers have not provided enough data for a user to do that. (IMO)