Doram I’ve been using that technique for nearly a year. Once a month, I purge the steam boiler in my MaraX, through the water tap, and refill with distilled water. The residual water left in the boiler provides enough minerals to the distilled water so the level probe still works. I run tap water here, which is approximately 120-130ppm hardness through a charcoal filter, and the 70l resin filter from Lelit, which I recharge weekly using a salt water bath. I try to monitor any scale build-up by checking the mushroom when I grease the cam and the water tap when I drain the boiler.
I don’t think this solution is 100% scale free, but I haven’t noticed any build-up in the areas I’ve mentioned.