Yeah it can be really tough. The tricky thing is finding a puzzle that a good majority of people (50-70%) can solve without hints. It's also super unpredictable to determine what people will find tricky. I thought today's puzzle was relatively straight forward, it's EYE -> TIRED. But now I'm realising that EYE has so many compound words which mean N blind alleys to explore before you land on the correct path.

And yes, TwixT does look like a really novel game! I've never really seen a peg board style board game before. I'll try find an old copy on eBay and give it a go.