To be fair, the SCR/AdBlue solution has proved to be the most reliable and effective in reducing NOx…a lot of the mechanical woes suffered by MAN, as one example, were caused directly or indirectly, by high-ratio EGR. Then there was the VW Lean NOx trap…which was the cause of dieselgate.
I know there were reliability problems with Euro IV SCR, but less than there was with the same-generation of EGR-only engines. Scania, which was all EGR back then, is now predominantly SCR-only.
If you buy AdBlue in bulk, the cost is buttons.