This! I use my HP 15C all the time. Reverse Polish is the only way to go. No parentheses, no equals signs, just start at the inside and work your way out.
I've had the 15C since 1985, and I dread the day it dies, because nobody makes a calculator with RPN now. Oh well, I've still got the old Pickett slide rule too, and log and trig tables in the CRC Handbook.
Apparently the are still available from HP, but made elsewhere.