I've been researching this method....I only found so far about the same thing you already told me.
1. Potassium manganate(VII) solution is chosen because manganate(VII) ions in acidic solution are a strong enough oxidising agent to oxidise Fe(II) to Fe(III) and the reaction is quick and quantitative.Secondly, because of the change of colour, from deep purple to almost colourless, when manganate(VII) forms Mn2+(aq), the titration is self-indicating. No indicator needs to be added as the (almost) colourless mixture turns pink at the end-point with the addition of the final drop of manganate(VII).
Potassium manganate(VII) is a solid that can be obtained reasonably pure - pure enough for work at school level. For very accurate analyses, however, it is not used as a primary standard and solutions need to be standardised, using e.g. oxalic acid.