Low Temperature mixed side radiant injection pump issue

rosy

This ? concerns a mixed lower temperature zone that I had planned to use a Tekmar 722 w/ motorized actuator and Tekmar 363 control. On the advice of a very knowledgable radiant specialist who posts here regularly, I am scrapping the 722 four way valve and switching the plan to a Grundfos 15/42 injection pump run ostensibly by the 363 (which it originally did years ago). Piping is 1.25" copper, horizontal "U"with 3/4" for the injection piping through CST's.
Question is this. Rather than use the 15/42 and Tek 363, I was wondering about using a Grundfos Delta T Miximizer or a TACO VT 2218 Delta T pump, which is about the same size but is programmable to run the temperature where one wants it. Besides the facts that this very knowledgable specialist advised against it, and I do have both the 363 (which has outdoor reset) and the 15/42, HAS ANYONE OUT THERE HAD ENOUGH EXPERIENCE WITH EITHER OF THESE PUMPS SUCH THAT THEY FEEL COMFORTABLE ADVISING ON THEIR DURABILITY AND EASE OF USE?

hot_rod

With injection mixing you need two circulators, the injection, and system circs.
The Taco I Series valve seems to be a popular solution for mixing valves with ODR. Then you could use the ECM circ of your choice.

Injection mixing with circs is not so common these days.