I am currently a Swashbuckler 7 / Paladin 2 in a RotRL game. I didn't plan to take paladin levels to start but I did intend him to be a pseudo-paladin, living a virtuous life and spreading the word of Shelyn. After a certain chapter in book 2 that forces A LOT of saves I said "screw it" and did the multiclass. I don't regret it, but I was already playing with a code anyway and there are definite downsides. My saves are amazing now (and almost every boss seems to be a caster of some sort) but I am two levels behind the gunslinger in deeds and I won't be able to take Signature Deed until level 13.
Ignoring saves, you'll be fine. You'll be weak until you get Dexterity and level added to damage at level level 3, you'll be really powerful at level 6 when you have an extended crit range (achieved at level 5) and get a second attack and you'll still be effective but slightly less so starting around level 8 or 9 when the enemies because bigger and have larger attack bonuses (meaning your parry works less).
Around level 6 my DM regularly called me overpowered because parry/riposte is very powerful at that point. Everything is medium-sized with mediocre attack bonuses and you get what are basically a lot of free attacks out of it.
I have no idea what it is like at 10+ but figure things continue diminishing as enemies get bigger/badder and magic plays a more important role. I expect my character to always be effective but I'll be limited to doing things that melee characters do.