FWIW, I've used third party blocking apps for years and have had very good results. A newer feature is a weekly sync with the FCC spam list. Any call detected from this list is auto blocked. Another nice feature is private or unlisted numbers can be blocked automatically if desired. I block these as they are usually always spam calls anyway. It's good the HTC 10 has an easy way to block as this is sorely needed these days, but 3rd party apps are very good and take it to the next level and beyond. Also, all your blocked numbers and other settings can be saved and downloaded to any new phone. Some very good ones out there. Extreme call blocker is the one I use.
Just my .02