I like straight razors and have a couple; shaving with them is very satisfying. I used one on my legs once, and I don’t have any horror stories to share, but it was an incredibly long process. It’s exhausting to be that focused & mindful for that long, and since my habit is to usually do a fresh shave the night before a triathlon, it just didn’t line up. (I guess some people talk about shaving legs the night before the night before a big race, but I usually don’t have the time.)
Also, very few straight razors are stainless steel. One of the few things that can really shorten the life of a carbon steel blade is bringing it into the shower, so you’re looking at a fairly radical shift in approach if you wanted to use one. A safety razor works quite well (and is definitely easier to use on the back of the knee), doesn’t require as much focus, and since the blades are just a piece of steel, they’re more suitable for recycling (if dealt with safely using e.g. a blade bank).