You get tools to make it even easier. More instructions, a sample bottle, more CYA reagent, and an optional salt test. Every update to the PS-2xx series is nice.

Do you NEED it if you have the PS-233? Not unless you are having troubles figuring out how to use the PS-233. You may need reagent refills, but Ben and Taylor sell those as well.

I actually have a bunch of kits:
PS-232,
PS-233,
Leslie's FAS-DPD and Total Pool care kits (together they are similar to the PS-232), made for them by Taylor,
the WalMart HTH 5-Way kit,
another DPD-based test kit (mostly useless),
several little OTO kits
and lots of reagent re-fills.
Plus, I DO have strips--that's how I know how bad they are.

IF you know what you are doing, the tests in the top 3 on the list are equivalent and you will get similar results. The 233 is a bit nicer than the 232, and gives you a different and better pH test--plus more refills.
The Leslie's combo gives you acid demand and base demand tests (which are nearly useless and very misleading--I never bother), and the DPD-FAS also tests for Monopersulfate (is that right?)

I have used all of them...That's why I call the WalMart the VW beetle of good test kits.

But do you NEED to upgrade from PS-233 to PS-234? No. Will it be a nicer kit? Sure! But if you are using the PS-233 correctly and have ample reagents, you are FINE!