Puff browser is not exactly a full browser and has a google2 patent. FF allready optimize their code for latin-1 and they say that utf-8 it's a mess... Fennec is more fluent and may have a better connectivity since v9, works better with Max VPN due to a bug fix for slower 3g connection. Opera test latest products for H speed only and is hard to say what's cookin' for Blink since Chrome works better anyway.
OK, the real fix is: Do not use Turbo or use Brain 1.0 to inspect Opera seeting for Turbo and sweitch off if enabled.
@dirgas In this case you request a browser 'fallback'
Yes, you may call it fallback. I call it failsafe
Local IPs are wellknown by IANA. See https://tools.ietf.org/html/rfc1918
A internal lookup table should be in Opera Stable, to disable Turbo for private IPs.
There's a way. If your site connection is via HTTPS Turbo/Off-road's servers won't be enabled on it. AFAIK it won't touch PNG images too.
There's no point on imposing that limitation to the visitors of your site, as Turbo/Off-road won't change any code nor request the mobile version of it, only save data by compressing it.