Munch wrote

Been toying with the idea of getting one of these battery pack jumper
thingies like this one on the Bay of Fleas: http://tinyurl.com/hzczdkp

Any preferred brands?

Nope, havent tried enough to be able to say that.

Does that one look like a good one?

Yep.

Are they worthwhile or just a 'toy' that doesn't work particularly well?

No, they do work very well indeed.