I tried on my phone and tablet through the Play Store. There are many similarly-named apps, but no ES File Explorer. What happened to it ?
Its on xda, which should have better curation than play store.
If you don't trust any app, you should remove it.
It is actually available on play store too for a price of Rs.380 for people who want to support the developer as it is quite popular on xda forums but donation is only available via bitcoin which many can't do.
Ditched it long back. Became too heavy and bloatware.
Yes, Solid Explorer is the most used by Rooting community, where they know what file they are changing for customization & tweak. Not for Naive users though.
Yes it has and the same features are also present in other File Explorers. Only thing is to be cautious while using Solid in system partition because it gives more privilege to users in system r/w access as compared to other explorers.

I tried the file sharing in FX Explorer today.
I use Files by Google & it is quite good for transferring between mobiles, have you tried it.
Its not that good compared to MiXplorer IMO. I create ftp server and hotspot (if required) and don't need to turn GPS/bluetooth on to share files. This is another app I use to quick share stuff between my own devices:
I know it is not as good but for a typical person not knowing anything other than app install from playstore(useful if other device belongs to such person), it is fine(mixplorer playstore version is not free).
does Xplorer still have that Bluetooth explore feature for copying files from other devices?
Nah man for sending APK you have to use something else like Xender.
Apk are easily available online. so sending is not preferred over wifi now.
No.. you can send apks via bluetooth by renaming extension to something else like txt mp3 mkv etc.
Exactly, now no one share apps and music and docs unless it's big size or more in quantity. For that you need to have proper file sharing apps.