Ignoring Ecotech - dosing Kalk into a return pump is not recommended (as you already know since you mentioned it here). My point is that even Royal Exclusive notes in their documentation to not do this. Then again I wonder how many people actually read those these days
For what it is worth I also fall into the camp of redundancy to include using the same pumps for other jobs like running a skimmer. This way I have redundancy and also a hot spare if I need to swap and one isn't stored away. Can still be a bit expensive when using named and not overseas knock offs. Having said that I did find surprising build quality differences between pumps.
I've used a Jebao DCT- 15000 which didn't make it past my displays leak check. Crack on the output neck. Maybe manufacture defect, not sure. Overall very thin material used so never went back. Neptune Cor 15 and Cor 20. Heavy duty, thick body and parts. Still in service today without issues running 2 returns and 1 skimmer. I am moving to a Royal Exclusive pump (single) for return prepping for a future display change and it is built even beefier than the Cor's. Body to impeller shaft.
I think there are a lot of choices so budget, display life cycle plan, and prevention of failure is key (redundancy vs cold spare, etc). You already know this - sorry. As I read your kalk reply I was like yep - even in the instructions which then got me on this rant.
Sorry.