League of Legends (LoL) Question: Should I use Yasuo in raked flex for promotion from Silver to Gold

Depends. Are you well versed in how to play Yasuo? Are you mastery 7? If the answers are no, then probably not. Don't play anyone you aren't solid on if you intend to win.

I would recommend only picking up a champion in ranked that you have a lot of time invested in to learn the nuances of the kit. More complex champs take longer to learn but can be a lot more powerful and rewarding to play. I'd recommend getting at least mastery 5 on a champion before you bring them into ranked.

Yasuo is good if you can handle him

Best pick him up only if you are very good with him and again then only if your team has at least one knockup. Yasuo tends to be a champion that will either become so fed, he will 1v5 or will starve so terribly he's technically playing for the enemy team. I'd advise you to veer away because of how fragile his gameplay is, but again, if you have practiced him extensively and your team has knockups, he's good for ranked. I have Yasuo lvl 5 and one lvl 6 token but I am not nearly experienced or capable enough to play him in ranked, even though I know most of his tricks. You may also want to remember that in ranked play, people are more likely to focus you down because of Yasuo's strengths. But to give you a straightforward answer, I think he's a double edged sword: he will either carry, or fail horribly. The reason why I'm recommending you to pick him only if your team can provide knockups is because, that way, even if you lose your lane, you will still be a terrifying presence in the late game. All in all, every champ can be played in ranked, provided you FEEL the champ yourself.

It depends. I'd recommend picking a 1v9 champ (since teams doesn't exist in such elo) like UDYR or jax. But honestly, you should pick whatever you play the best. Its not worth going a champ that is considered to be stronger than the champ you really play good. Pick your main, feed yourself up and say hello to gold :D For the exact question, Yasuo is 1v9 champ and if you play him well than HELL YES you should