The HP-35s is a great calculator in the tradition of RPN. Some caveats:
1. There is no built in polar-rectangular/rectangular-polar conversion. Yes, complex numbers provide a work around, and you can always program it or use the HP provided program, but it's really not the same. See 3 below.
2. Total membory of 30k? In this day and age, that's downright puny.
3. There is no capability of storage for programs, data, etc. That makes it a chore to reload programs.
4. The display can be hard to read. Strange considering the great displays that HP has had in the past.
All in all, a great calculator, one that is a pleasure to use, with tremendous functionality. Especially likeable are the tactile keys. Just for context on this, I am a practicing EE, with over thirty five years of professional experience, and have been dealing with HP calculators since the HP-35.