I don't particularly like the base game swimwear except a couple of items. I rarely use the pattern bikinis or the swimsuits except for background characters.
I wouldn't call it a must have kit, compared to Moonlight Chic, Incheon Arrivals or Fashion Street which are all awesome kits IMO. But my Sims always have at least 3 sets of swimwear or more depending if its a Sulani household. So I thought might as well as I'm running out of combinations. I think of the 2 kits Modern Luxe is the better of the 2.
I highly recommend @gooochyeee's excellent review of that kit too!☺️