i have seen the sawyer pump/extractor. it is sold with the premise it can remove the venom through the original wound. it is actually a neat looking little kit but the problem is that venom can be injected so deep and dispersed through different tissue planes that venom return is low. if the venom gets into a vascular structure it is long gone before you can apply the gizmo
it is not "harmful" in and of itself... as long as you dont make incisions which can cause significant bleeding (pit viper venom has anticoagulants in it) as well as the risk of damage to important structures like arteries and tendons etc. i have seen some wounds made by people in the field (and in hospitals) and they can be worse than the bite itself !!!!!!
as far as what to do 300yds off the road with a bite...get out as fast as you can. it is ok to gather yourself but with a serious bite you want to get out as quickly as is feasible. trying to call for help is worthless unless you have a sat phone or a field radio (neither of which i own). some of the streams are so isolated i dont see anyone all day and waiting for rescue could be futile.
if i had a serious bite and couldnt get out i would hope i was on a river by a major trail and hope someone came along.