Let's discuss the concerns you raised..
1. Temp sensor not in-sync
I believe my new chiller have a feature to calibrate the thermo sensor (will let you know). The build-in sensor senses the temp of the water in the chiller whereas the external probe senses the temp of the water. Of course there will be a different in both reading. However if you calibrate your chiller thermo sensor to be in sync with your measure temp in your tank, that will fix your problem once a for all, without having to invest in the external probe.
2. Titanium coil crack because of freeze
If you do not have an external probe then obviously this will not happen. Even if you choose to have it, all you have to do is to set your chiller temp a bit lower than that of the desire temp (which you set on your external control). That way there is no way to screw things up.
Now.. why would anyone want to use the 'delay' function??
Someone said (was it you har?) that even if the chiller delay kicking in by 2 min, there is no change in temp and there will be $$ savings.
Well, yes and no.....
'Yes' because that's what you see on the digital display and you assume that no change in digital display ==> No change in temp.
'No' because in actual fact, there is a rise in temp because your tank is of a lower temp than the surrounding and heat transfer will always happen (law of thermodynamics).
So let's say you delay the kicking in of your chiller by 2 min. In actual fact, your tank has already 'suck in' 2 min of heat.
Assuming your chiller is set to start at 26.0C and stop at 25.0C, with the 2min delay instead of 26.00C it is now 26.08C when the chiller starts to work (and to you, it is 26.0C).
So your chiller will have to work from 26.08C --> 25.00C, instead of 26.00C --> 25.00C.
Going by common sense, the chiller now have to work longer than before, right?
Any saving, if at all, should be very small in comparison to the investment to buy this external gadget.
So is it that worth it to buy an external gadget just to save that few cents per month, and have all kinds of wiring, probe and gadget hanging around, plus the fear of your titanium coil cracking (if you don't set it up properly)?
Maybe someone can try to convince me (and others who agree to my argument here) why this additional gadget is useful, other than making a few more hundred bucks from me..

.. like some LFSs....

.....
BTW, who rated this 4 stars?
Are you sure it is 4-stars and not 5-stars postings? 
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