Need advice from Engineers who are also TI users

[ijabbott]

I'll third the Casio fx-9xxx and CG series as worth a look. I have a CG50 myself.

You could also take a punt on one of the unofficial "ghost run" manufactured HP 39gs calculators available from Chinese sites such as AliExpress, and from Chinese sellers on eBay. They are fully working, without serial numbers. The keyboard seems to be the same quality as HP 50g, but the display is smaller and has fairly poor contrast compared to the 50g. They are available for nearly throw-away prices though, so if you don't get on with it, it's no big deal.