Yep!.You won't find it in your Google Play Store (why would you?).

X-years back it was Amazon that made that Promotional Freebie directly with their Amazon consumers, and not Google in any way at the time?, or since ... (until now at least?)

As per my original first comment above ... (I got this for freeeeeeeee too, via the same Amazon source some years back also, lol).

But for only 10p?.

For the whole better Google Store 'flexibility' aspect thing of it all and stuff? (over that of my rather current, but yet not as flexible Amazon equivalent), I'd be more than ok with giving up my 10p for that ... :-)

Ps. my 10p will reach it's more productive usefulness as such in a few days time (I'm on pure Data Allowance at the moment, and don't want to potentially kill myself if the download is a killer also?, lol.

But WiFi Internet in the next day or two ...

Unless that is, someone can assure me it's file size is like only 10-20mb or something?, hehehe). :-)

Hehehehehe, probably ... :-)

Hehehehe, don't worry about anything!, I too was originally clueless to the whole Amazon Underground thing when it first launched too!.

Back in the day, all I remember was Amazon Store plastered everywhere on both the insides of train stations + plastered within the body of the trains themselves on my way to work ...

Then suddenly out of the blue (as if literally from nowhere, BAM!), Amazon Underground suddenly came/entered the mix!.

Initially I was like what the hell?!.Had no idea that the 2 different entities were kinda like basically synonymous with each other?, so to speak (though I did suspect such regardless?).

What was once Amazon Store, HEAVILY then migrated, and upgraded itself to become Amazon Underground!.

But with one MASSIVE DIFFERENCE!.

The original Amazon Store (like the Google Play Store before it), had BOTH free + paid for App's upon it ...

But the Amazon Underground does NOT! (it's mainly awash with otherwise paid for App's, but ALLLLLL for free!!, worth taking a notable note of that aspect of things I reckon?). :-)

Other traditional freebies like IMO, Kik, Viber, Tango, Skype, HUKD App and the like, are still alllll on there too/anyway, regardless?.But you know will also have access/exposure to now traditionally paid for App's (eg. like the OP's above App, the former Premium version of PLEX, Smart Office Pro + MANY many Tools, Games, Utilities + other App's, etc, etc?) beside too!. :-)

So yes, by all means, rock both! (interest, necessity, and/or internal phone storage allowing, or whatever?), and see what's what ...I hope that helps answer your question somewhat?, hehehe. :-)

Only my own experience, comes preloaded on sony phones I’ve used and you can’t remove it but it constantly sends you push notifications suggesting you upgrade to pro. Really annoyed me as you can probably tell.