If you are fairly fit, have the right light but powerful saw and know what you are doing, then you've got to be into some pretty gnarly or high up stuff to make a tree shear worth it on a smaller machine IMHO. 5 or 8 ton maybe, 3t I'd say only for specific tasks such as topping out a hedge.
Are you burning on site? How much of the stuff like the above do you have to do? I'd clear the stuff in that photo to a well burning fire in around ten minutes with my E27 and saw.
If the fire is a way away, a great technique is to fell the trees (bunch the multi stemmed stuff with the grab first and apply slight upward pressure then cut through it all at once) then drag as much as you can (like a skidder) to the fire, where a second bloke cuts it to the required size and takes out the unions, which is the most important bit of keeping a fire going unless it's whole tree sized. You return to collect another load, and when you drag that back it takes just thirty seconds to clear the cut stuff onto the fire before you drag the next lot into place for cutting. Have a petrol blower injecting air via a cuttering pipe into the fire, and saw bloke can keep an eye on that too, as positioning is critical.
Basically, it's really easy to cut that size stuff and drag it about, and I reckon a bloke on a saw is cheaper and faster at sectioning it to the required size.
At 8 ton size though, that's the sort of stuff that you can swing onto a large fire whole if you have it going hot enough and can keep it fed fast enough.
Oh, and with those brambles, grab them. Then put them down on some more brambles and grab again. Repeat and you will end up with a ball of brambles you can barely lift, as the brambles in the grab helpt it to trap more with each bite. Gets a large amount of the roots out too.
