My personal opinion is if you dont install anything from any dodgy back alley websites you should be fine security wise. Although there is risk, im not going to loose any sleep over it.
Real down side (for me) is you have to run though hoops to pass safety net checks for certain apps to work (including extra hoops for banking apps and google pay to work). Also root isnt supported by the devs here (which is fair enough).
If you arent experienced with rooting and fixing the downsides i would recommend you just use privatedns to point to an adblocked dns server ( For my kids i use adguard dns).
If it was for just adblocking i would use the dns route but I cant live without CustoMIUIzer for tweaking settings etc.