Being a bit of a Luddite, I go for the tell-tales option myself. For wind strength I use Admiral Beaufort's tables. Though it's not often you see a fishing smack these days.
Not really except for the racing boys. They derive polar diagrams of true wind angles and speeds for different wind strengths. Initially, they may use manufacturers published data, then tune it to their own boat performance as they develop new sails etc. All things need to be equal so they go for true wind when doing this.
Whilst they sail, they are constantly checking their performance against the polars to make sure they are sailing at optimum speed and trim/steer for best performance. Having said that, I haven't raced for many a year so stand happy to be corrected.