I play every slot before I write about it. That starts in the demo, usually a few hundred spins, to see how the base game behaves and how often anything happens at all, and it continues with real money when a feature is worth paying for.
The numbers in the fact panel come from the game itself or the provider own sheet, never from another review: RTP, volatility, reels and rows, ways or paylines, and the bet range in EUR. If a slot has more than one RTP version I say so, because the copy you land on depends on the casino. Bonus buys get the same treatment where they are allowed, and I note what the feature actually paid rather than what the maximum win says is possible.