I am in love with the RS, and it's coming from someone who always hated things like "Power Rangers"
So, that says something.. doesn't it?
I'm one of the people who believe that Sanji wearing the RS shows "MORE GROWTH" in his character compared to him denying it and not wanting to use it.
And the fact that he decided to use it "without him cornered in difficult situation to use it" is proof of his "growth" as a character. There is a difference between using the power by your own choice, and being someone who continue to whine and deny using it, only to use it when you are in bad situation, and be hypocritical. It shows your word has no weight.
On the other hand, Sanji accepting his past and ties to Vinsmoke, and using this power for the benefit of Woman's bath... Sorry, I mean for his nakama, alliance, and to have higher chance of victory at the cost of denying just for pride and maybe decreasing his chance of victory and being less helpful for his nakama! It's the RIGHT CHOICE. And it shows great growth by Sanji's character that he's willing to put aside his pride, and willing to put aside his hatered for Germa for the sake of being more helpful for the crew.
After WCI specially, he OWES THEM that much.