There should be some boost with his kicks if he uses those jets from the feet to accelerate them.
Yes, against blunt force is useless and it only can resist cutting/piercing attacks around those special bullets AP. His CoA > the suit in that regard and at the same time it protects him from blunt attacks.
Neither was the RS highlighted as some strong armor (it was Germa's bodies).
The part which was highlighted as something which grants actual durability boost is the cape with its function of a shield (Sanji's statement and Germa used it to protect from the guns when they protected Capone and Caesar).
Invisibility? CoO counters it
That depends on the user's lvl of CoO.
It's not the same to sense him and knowing his position than doing that and algo sensing his attacks accurately (like in DB where they know how to sense accurately their enemies by ki and can fight them blind folded). And one needs to have experience fightning with invisible people as well since even if you can sense them with CoO it won't be the same as seeing them directly.
And none of beast pirates seems like a CoO expert, they are all more focused on brute strength (all Zoan) so most likely they specialize on CoA.
Boosters? Sanji already knows Geppo.
Here depends on if he could combine both somehow and achieve greater speed with the two of them at once.
Floating devices? Meh, maybe kinda useful to stay in the air without kicking.
Not really useful since Sanji didn't show fatigue or something like that because of Geppo using.
Depending on some functions, the RS might be a good boost for combat.
The invisibility function is a good PU but for now he only used for testing it, for the gag and for infiltration.
We need to see what use will Oda give to the suit overall from now and then we can say if it's a weak or strong PU.