Buying second hand dive computer

[Subcooled]

After cycling through 3 or 4 lesser dive computers I've ended up with a used Shearwater Perdix AI that I bought for $700 here on the classifieds.

It's a good device.

Those who choose to dive tables and disparage computers are fighting a losing battle against practicality and progress.

It's not a loosing battle. It's a trade-off.

If you buy a cheap computer now it is almost guaranteed that you will be buying a more capable model soon if you continue diving.

This, again, depends on your budget and on your values. Could be true for many, though.
A true minimalist would wear a dive watch and a depth gauge only. Liveaboards would not like that. And dives per day would be limited.

But, if money is a prime issue

then you can do without a lot of expensive gear... but then there will also be some real limitations... or a planning nightmare.
You probably made a good choice.