Same here, I hesitate to install apps outside of Google play. I also use Google play reviews, rating and number of downloads to gauge quality of app which is not possible if you directly install.
google play is not really that reliable to be honest i think apple store is still the one that is most picky when it comes to applications they will display meanwhile with google play i know some applications that are still quite suspicious and not properly reviewed by google play themselves or at the very least have a good quality
I don't consider apps on Google play safe (or iOS store for that matter), it's more like being able to judge app's legitimacy by what info Google play shows (i.e, rating, reviews and downloads) — it's better than directly downloading from third party site where there is no such info available.
Regarding iOS store being better in comparison, that may be true, but it's still better not to blindly trust apps there as well, since there have been cases where fraud apps made there too.
...and no I have never used casino apps, I stick to websites as long as they get the job done whether it be casino or otherwise, as I like to keep my phone storage free as much as possible.
that is one factor to consider if you have a device that is low on storage and does not function well with big apps it will just be an inconvenience to use them
No, even if my phone has enough storage (which these days all phones do), I prefer websites, I mean why bother with app if website gets the job done.