Is playing a slot in demo mode a useful test?

Demo mode reliably shows mechanics: paylines, feature triggers, bonus-buy rules, hit patterns and whether you actually enjoy the game. It shows nothing useful about your odds of winning money. Demo sessions are far too short to reveal RTP, they carry no financial pressure, and some providers have historically served demo builds configured differently from the real-money version, which several regulated markets now restrict. Treat any streak in demo play as noise, in both directions. The honest use is deciding whether a game deserves your stake at all, and reading the paytable and maximum win before real money is involved.