I've only used the tree puller and it makes quick work out of trees the sizes you mentioned, however I use it on a skidsteer and have a good view of the end of the jaws. I've never used one on a front loader and not sure how good you could see. Of course after using for a while it would get easier.
It would seem you'd need visual contact with the shears position more than you would with the puller and to me it's easier to fill in the hole left with the puller than to deal with the stump left with the shear. Of course thats just me talking.
Now about the question of the pine tree pulling I've heard a lot of people talk about how easy pine trees are to pull. Maybe I'm doing it wrong or different kind of pines but I fine them a struggle to get them out of the ground. They have a straight down tap root much longer than oaks, sweet gum, or any of the scrubs such as hedge and tend to break off instead of wanting to being pulled. If you rock on them to much they will break. I have clay ground and sure that's a factor.
I see in you Avatar you list as having a 4500 backhoe. It would be slower but a lot of work can be done with a thumb. That's how I cleared around the fields and field roads before the skidsteer days. My backhoe is a IH 260A about the same size as yours. After pulling for a while just turn around and fill in holes then when you drive off you are DONE. I couldn't imagine doing 20-30 acres like that but it could be done. That would be a lot of therapy as its a smoother ride on the backhoe all day vs working with the front loader, and for sure smoother than with a skidsteer.
Sorry for writing a book, I got excited as I've been cooped up here for over a month with no seat time. It'll take a long time to dry out around here. Good luck with your decision.