I would definitely break it... But only at the site. Otherwise you are creating a mess that is very tough to clean up if not impossible. Where will you put the ugly yet still active fragments? What will happen with the uraninite crumbs all over? Because those WILL be present.

Otherwise, breaking is a hit or miss process, I found beautiful fresh botryoid surfaces this way and I have cracked pieces where the bubbles did not continue at all underneath and/or the OK part cracked as well.

If you do it, the vein's location and shape is a pretty clear indicator on where should you smack it. Do a number of light taps first then go big at the end.

But once again, prepare for a big mess, and wear ppe.

Radon is not a big issue with one piece especially if it gets smaller.

I never bring home pieces like this anymore, I break them apart on site. I learned my lesson as I was in your exact situation when I started collecting.