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For a few extra dollars, prefer the Ti 30x Pro if available. It has many more functions - tables, vectors, certain integrals, derivatives, in the same package. The big advantage of it (as well as the Pro and generally the Ti) compared to Casio is that they do not lose the formulas and data you have entered when the calculator is turned off. Casio calculators usually turn off automatically after 10 minutes of inactivity and erase everything that has been entered up to that point, such as formulas, statistical data, values in tables, etc... I am not referring to Casio models that can be programmed or/and have graphics, and I reserve a caveat for the new series that end in -cw.

Competitive with the Casio fx-991ex. Comparative:
Advantages of Casio:
Casio solves systems of equations up to 4x4 while the Ti only does 3x3.
Casio has excel (albeit basic) while the Ti does not.
Casio is less bulky than the Ti.
Casio has built-in prefixes m(illi), μ(icro), n(ano), k(ilo), etc. while the Ti does not.

The same:
Build quality.
Both are solar-powered (Ti is not visible in the photo).
Similar speed in complex calculations.

Advantages of Ti:
Ti retains calculation history even when automatically cleared, while Casio does NOT - the entire history is automatically deleted. Perhaps the most significant advantage of the Ti!
By repeatedly pressing a button on the Ti, you get different functions. In Casio, you have to press Shift+button to get a different function.
Copy-paste into previous results on the Ti. In Casio, you must have them saved in memory.
Better screen resolution on the Ti (more readable).

Differences:
In the calculation history on the Ti, you can copy-paste from previous types or results into new calculations, but not edit (you can only edit the current type). On the other hand, in Casio, you can edit previous types but not copy-paste either into types or results.

Excellent but the price difference from the FX-CG50 does not allow it to be value for money as it has a black and white screen of lower resolution and smaller memory, 3MB compared to the 16 of the FX-CG50. Otherwise, similar menu (which requires familiarity) and capabilities - except for the 3D graphics.

There is an emulator for PC (90 days free trial) from Casio for someone to see how it works.

However, for those interested, it can also be easily converted to CAS (for symbolic calculations) through xCas (google it). The remaining memory, of course, after CASification is small ~0.5MB...

Cheap you can't call it, but for what it does-offers it is excellent! The best nonCAS that exists.
The menu requires familiarity if you come from simple scientific calculators, but the capabilities are endless. It has up to 3D graphics and micro-Python language for programming, as well as connection to PC via USB. Its 16MB memory is satisfactory and you can store not only programs or calculation types but also photos (after conversion with CASIO software).

You can download the Casio emulator from its website for computer (90 days free trial) and see how it works.

The extra bonus now: With a very easy process and a relatively small file of 2MB, you also acquire CAS (Computer Algebra System) for symbolic calculations (it solves even differential equations - symbolically). Search for xCas on Google.

Excellent for its price! The second best among the non-programmable calculators on the market. (the first one being the 991EX).

P.S. Crazy market fact: This version (the second one) is 10 euros cheaper than the first one!!!