I'd never heard of Startone before you mentioned them, and I'm reluctant to comment on any keyboards I'm unfamiliar with, beyond pointing out whatever information is in the manuals. The only information I could find out about them seemed to come from the Thomann mail order company (
http://www.thomann.de/gb/startone.html), although I'm not sure what connection-- if any-- exists between Startone and Thomann. The manual for the Startone MK-300 is available in PDF form from Thomann's web site (
https://images4.static-thomann.de/pics/atg/atgdata/document/manual/c_343081_r2_en_online.pdf), and every page of the manual has "Thomann" printed on it, as though Startone were a division of Thomann-- except the way Thomann talks about Startone seems to indicate that the two companies are unrelated as far as ownership, so perhaps Thomann has a special deal as distributers of Startone's products?
Anyway, the MK-300 looks like it might be a good buy as an inexpensive beginner's keyboard, but I don't know it sounds, as I can't find any videos that show it in action. It seems to be roughly comparable to the Yamaha PSR-E253 in terms of the number of sounds and styles, but it has twice the polyphony of the PSR-E253, it has touch sensitivity (whereas the PSR-E253 does not), it has a USB port for connecting to a computer (whereas the PSR-E253 does not), and it has a pitch bend wheel (which the PSR-E253 does not).
One thing the MK-300 doesn't have is the ability to modify its built-in sounds using MIDI Control Change commands for Attack Time, Release Time, Filter Resonance, and Filter Cutoff, which the PSR-E243 does have (although the PSR-E253 does not, since Yamaha removed the USB port on the PSR-E253). On the other hand, according to its manual the MK-300 is able to respond to MIDI Control Change commands for Portamento Time and Portamento On/Off, which the PSR-E243, PSR-E353, and PSR-E443 are not able to do, so that implies that you could use MIDI commands to get portamento effects. However, the MK-300's manual implies that it can't be put into mono mode, which is usually required for portamento, so I'm not sure whether or not the MK-300 can actually do portamento. And in any case, it doesn't matter whether the keyboard lets you modify its sounds and/or play portamento via MIDI Control Change commands if you won't be connecting it to a computer during performances.
One thing that's missing from the MK-300's manual is the list of Bank Select and Program Change values for each of its voices or sounds. You should be able to figure them out for yourself by connecting the MK-300 to a computer and monitoring its MIDI output as you scroll through each sound, but it would have been nice to have that information provided in the manual.
The good news is that Thomann says they offer a 30-day money-back guarantee, as well as free return service-- but only if you're in Germany. I don't know if you were thinking of ordering from Thomann, but if you order the Startone MK-300 and then decide you don't like it for some reason, you should be able to return it and get a refund-- although you'll have to pay for the return shipping (unless you're in Germany). It's always best to actually try a keyboard out before you decide to buy it, but if there are no stores in your area where you can "test drive" the MK-300 yourself, then making sure the vendor you order it from has a money-back guarantee is a must.
PS: As far as Casio keyboards, I have one Casio, and I do think my Yamaha keyboards sound better than my Casio-- but I have an older, inexpensive Casio model, so I doubt that it sounds as good as the newer Casio models. Casio keyboards seem to offer "more bang for your buck" compared to similar models of Yamaha keyboards, and there are some keyboard players who seem to be pretty devoted to Casio-- especially their digital pianos. But again, it's always best to actually play a given keyboard yourself before you decide whether or not to buy it.
