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[parisse]

factor(x^202+x^101+1) takes 11.6s on a Prime, you probably did not check with the right input or you did not make an exact factorization with integers coefficients. It takes about 40s. for Maxima on my htc smartphone, on the same phone Androcas (with giac kernel) takes 2.7s. You should not benchmark by doing several times the same input, since some CAS are not recomputing with the same initial input. For the classpad, I'm not certain the comparison is meaningfull, giac and maxima certify that the factors are irreductible over the rationals, the nspire CAS does not.
Also try factor(2**128+1) on maxima and ifactor(2**128+1) on the Prime.
If you have example where maxima is several times faster than giac, please give them, because it means that the giac implementation should be improved.
Now about the UI, just try a Prime (or a TI nspire or a Classpad) and compare with maxima on Android, with someone who is not a CAS expert. Or compare maxima on Android with wxmaxima! Even if you know perfectly the command syntax and you know what you must type in the commandline, you will have to switch keyboard from alpha to numeric several times, and if you make a mistake you don't have left and right arrow on Android. For me and probably for almost everybody, Maxima on Android is much much less usable than any CAS calculator.
About octave: I don't speak about numerical matrix operations, I'm speaking of all you can do with a CAS: algebra, calculus, arithmetic, exact and approx linear algebra... Octave is a numeric package. I just installed octave to test on my smartphone, now I run it, first I get a windows that asks for money (annoying), then all I get is a terminal output, no easy way to get help how to enter commands. It's not symbolic, if I enter x**4 I get x undefined. Perhaps you can plugin some symbolic soft inside but which one?
If you are mainly interested in doing numerical matrix operations with large matrices, then it's different, because the screen size of a calculator is not large enough, you will need file access to store data, and you have much less direct interaction with data. But this has almost nothing to do with a CAS comparison.