Yes, I would say that RPN is very much still relevant today. It's a shame that it is not more mainstream than it is. Once you have learned RPN, you never want to go back to algebraic mode, especially not modern variants that somehow succeed in being stupider than older variants.
Its a difference between "easy to use" and "easy to learn". Often, these two gets confused and since algebraic mode are self-explanatory and easy to learn, people tend to stay with algebraich mode. But algebraic mode is NOT easy to use compared to RPN. You will save keystrokes (and thats important on a small interface such as a calculator), time and confusion as you develop a feel for correct entries, subtotals and validation of the results. Things like reciprocals and "out of order entry" of numbers gets much more straight forward with RPN and done correctly you never ever need to use parenthesis¹.
Nothing beats having a physical calculator, so don't bother with apps or desktop programs. There is a few ways to get hold of an RPN calculator. Vintage HPs and swiss micros are certainly quality, but the prices can be a setback and if calculator nerdiness is not you thing and you only want a calculator like everyone else to use on an occasional basis you can go for cheap. Searching eBay for RPN calculators and order by price yields many former Soviet calculators, mainly MK-61 and MK-52. They are both very decent calculators but the keyboard kind of sucks. You get used to it and learn how to handle it well, but at the beginning, expect unintentional missed and double-presses on the keyboard. So, if you are unfamiliar with both RPN and a el cheapo keyboard it can maybe be a problem to know whats wrong when unexpected results are given.
The newer HP-35s are perhaps the cheapest way to obtain a new western RPN calculator, but it have a few quirks that can drive you mad. Such as the "feature" (read "bug") that a number in floating point mode not always fits the screen and you have to scroll sideways. That's just sloppy design and inexcusable. You almost have to operate the damn thing in fixed point mode with a reduced number of decimals.
The HP-32Sii may be the best all-round RPN calculator, but sadly it typically costs at least $100. But if you happen to run by an working HP-32S at a lesser price, don't hesitate, buy it!
Learning RPN takes 10-15 minutes of hard work to commit it to your spinal cord². Then, you are free. Forever free. You won't lose your ability to use algebraic mode, but you won't prefer it and you will grunt and swear at the stupidity of it.
1) My English defies me here. What is parenthesis in plural? Parenthesises? Parenthesisies? Parenthesisessess? Any combo of 's or s'?
2) Or cerebellum I would guess.