With tritium sights, I've always avoided punches for fear of breaking the vial(s). I used to have a local gun shop that would install them for $15-20 so that's what I always did. Brought in a gun one day and they decided it was now $75 to install sights (direct swap mind you, no milling) so I figured that was the sign to buy a sight pusher. There are several options available on Ebay for pretty reasonable prices now, so if your local shop wants a lot of money to install them, I'd go that route.
TLDR: if the sight has tritium vials, a pusher is the safer option.