From my perspective, it's better to have all 4 tyres the same. But I know the Pirellis are not cheap tyres.
Toyos are very good tyres, but I don't know of anyone who has experience of Pirelli and Toyos on the car. The combination will probably be OK, but you'll be the 'test pilot' as it were.
In the end it's your choice:dunno:
David