Update : the rubber tips I got with the discounted nordic walking poles each wore through in about 50km. They worked well though. My alu poles seem to work their way through the rubber, perhaps due to their open ends, and the thinner diameter than the tips are made for. I did make the fit tighter with tape, but it may not have helped durability much.

Now I can only select one set of not-fully-worn tips, and no idea where to easily order "proper" carbide tips for my Swix poles. Of course just when I really get some consistency in my training...