ah i forgot:
just as wapiti points out, SMI and SPI are heavily dominated by the three big (Novarrtis, Roche, Nestle). SLI has them capped to 9% (?) each improving the diversification.
in addition there is a SPI mid ETF that allows you to diversify much better over 80 swiss mid caps. considering that all swiss blue chips are already in your VWRL (from Nestle 0.66% to BCV <0.00%) [source: p.42] it might make sense. I concluded this for myself when putting together my portfolio that also contains VWRL and SPI mid. however, i already consider swiching to IB & a different portfolio
\edit: i am conciously overweighting small caps in my personal portfolio
there is also a SPI extra index fund by CS, but it is available only for institutional investors.
interesting NZZ article (german…) i just found
\edit: available indices via ETFs (to my knowledge) are SPI, SLI, SMI, SMIM, SPI mid