how many players use GOG CLIENT?

No one knows GOG doesn't really release that information often or at all as far as I know.

Many do not realise you do not even need to use Galaxy in order to play. The cloud saving is not working in a lot of games and is a bit iffy anyway.

A wild guess: 82%

I'd suspect most people use Galaxy. The GOG website strongly nudges players to use it and frankly, I don't see much reason not to use it, unless you are vehemently opposed to clients in general or have a PC that lacks the resources to run it.

I do like the client actually, although I disagree with how GOG discourages users from having all their games backed up through offline installers.

As far as I know GOG doesn't release the statistics, though even if the real stats were posted, there would still be massive sampling bias in favour of Galaxy simply because Galaxy's telemetry is counted whilst offline installers aren't due to their nature. Example - let's say two GOG users buy the same game at the same time in 2014 (an old game that doesn't need updating much), and both replay the game once per year:-

- Person A downloads the offline installer and backs it up then replays it annually by locally reinstalling it offline from a backup drive. Those 7x replays will all be counted as "1x offline installer download" by GOG's server / account usage telemetry. By 2030, he'd have 17x annual replays yet all those will still only be counted as "1x offline download". Depending on Firewall settings, any potential "count this as one install" telemetry "pings" sent out by the offline installer could get blocked and not be counted.

- Person B replays it Steam-style by Download -> Play -> Delete -> Re-downloading it via Galaxy annually, will appear to GOG server statistics as "7x Galaxy downloads" by 2020 and "17x Galaxy downloads" by 2030 (for one user for one game).

So between just these 2x users playing the same game bought at the same time, the same number of annual replays, the Officially Correct (tm) download statistics will show "87.5% Galaxy vs 12.5% Offline Installer usage" in 2020 and "94.1% Galaxy v 5.9% Offline Installer" by 2030. Of course, actual real-world client vs offline usage between the two will still be 50/50 (one is using Galaxy, and the other isn't...) And this is why I've always found trying to compare "usage" statistics between Galaxy vs offline installers pointless when only Galaxy telemetry is counted and it encourages constant "Steam experience" re-downloading whilst a large amount of offline usage will always be "invisible" to GOG's telemetry and constant annual re-downloads unnecessary precisely because that's the whole point of offline installers by design...

^ This. It's like GOG's Galaxy telemetry = the equivalent of Netflix being able to count how many views, partial views, where you paused and for how long, how many multiple views in the same household, what subtitles you used, etc, for any Netflix movie, whilst GOG's offline installer equivalent = the store you bought a DVD of same movie from counts the "sale" of that DVD as "probably 1 view" but with no equivalent "offline telemetry" ultimately has no real clue how many times you re-watch it / other family members borrow it to watch at different times. So even if GOG release the "official" figures, I doubt you'll ever get actually valid real-world offline installer usage figures precisely because they're offline and won't be counted...

at least me. come on, I can't play my FTGs' multiplayer without it.

Depends on how they evaluate stats. I'm 99% sure they can also track and see only unique downloads (a simple yes/no for an account+game). I honestly find usage stats shared by most companies worthless in general, unless the exact method of measurement is stated.

Are you tracking all accounts since the beginning? What is the time frame? Are you counting dead/inactive accounts? Unique or repeated occurrences? And much more...

But true, companies usually like stating the highest possible numbers where applicable.

Example: World of Tanks claims nearly 6 million players. Now take away the accounts that haven't played a single game or haven't played a game in the last 5 years and I doubt it would be even half that number. But we can't know that unless they share the methodology behind this claim.