just using kodi, mobdro and a couple of other apps on my ADdroid tv box which I just stopped using cause of all the ADS...
also to answer your question about the apps and the app in question was some fitness abs app I don't recall what the exact name is but it was very intrusive and took over my GF's swipe screen to answer a call!... another note no offence but I hardly believe that you NEVER experienced this in the 3+ years you've been using ADdroid because I have had several friends go through some bad experiences one time or another and myself and my GF with rogue apps taking over their phones or malware and even viruses! also there is a plethora of articles and chat forums describing other horrors that has happened with peoples ADdroid phones and one app that I remember reading about was the messenger app for FB that was a fake one and hijacking peoples FB account and posting adverts and links to video's to all their contacts which happened to my GF and I had to search google to find out what the culprit was... maybe you don't install anything or almost nothing except those BIG apps like FB and twitter and snapchat and major gaming tittles on your phone which is why you've been lucky in the 3+ years you've had your ADdroid phone or something else that's not being said... but for all the MAJORITY of other users do get bad apps/malware and viruses... which is why there is a plethora of anti-viruses apps on ADdroid...
In all seriousness, nope haven't had anything pop up on my Androids unannounced or strange occurrences happen in that time, never not once. If I set it we let it, if I don't it won't. Yes I have had apps with small ads appear in place (mostly nonintrusive and far less sever than some websites) but if there's a choice to rid them by purchasing I'll definitely do so... GasBuddy was one inundated with ads and no option to purchase so I dumped it, can always visit website if the urge arises, or acquire that info elsewhere.
My Droids vary on the quantity of apps from 120+ up to 150+, device dependant - In comparison, my Windows Phone's sit at around 80. And yes I have the likes of Messenger, FB, Twitter, BBM and so on, been that way since day one. No games/gaming here whatsoever. IMHO it is all about the "INITIAL" setup and getting it the way you want it to be in the beginning (allowing, not allowing permissions, etc), a little extra effort at the start but it pays dividends in the end. Like I said, it's basically a "set it and forget it" affair or at least that's how it has been for me, might have to tweak any new app installed but found this to be rare... Ad versions not withstanding.
So from my experiences reliability, consistency and fluidity has kept true with only four hard resets being performed on 6 devices combined, that alone speaks volume to me... actually there were only two "musts" because of bad updates while the other two were due to my tinkering. I think my L950 almost exceeded that number of resets, if it didn't (lost count), in 2017 all by its lonesome.
Have never used an antivirus on my Droids either nor have I been knowingly infected. Remember when PCs were targeted so heavily way back when (still are), why do you think that is? Like anything the hackers are going where the "money" is. More user more chances of scoring big. Same would hold true for Android yet think the users themselves can a lot to mitigate those problems, going by my experiences doing so is pretty transparent taking no effort at all.