I am happy using a manual tool and you can feel for any issues, binding etc.
In a different vein, have you watched how people use tools, driving a few days ago I watched a workman helping a couple of young ladies change a wheel, the nut was tight and he was straining hard pulling upwards on the wheel brace, to me the logic was as a big bloke all he had to do was press down and use his weight with foot or hand, much less effort. My other pet hate is watching TV celebrity mechanics using an open ended spanner the wrong way on a nut, I was taught to turn in the direction that put the load on the strongest part of the spanner, if ever you see a broken open ended spanner it is always the short end broken, if it doesn't break, it can stretch the jaws wider. It's why stilsons only work in one direction.
I broadly agree with you on the feel a manual tool gives you, especially where smaller sized stuff is concerned. However when it comes to corroded fixings, especially if they are larger in size, I find using an air gun on quite a high torque setting to give it a brief shocking in the direction of tightening before then trying to undo it often meets with success.
On the subject of open enders I have to say I use them only if I can't get a socket or ring key onto the fixing. Although they can be useful once a nut or bolt is broken free, 'specially where access is very limited, to then work it down the thread little by little, half a flat at a time perhaps, by reversing the open end. My automatic choice, space permitting, would be a hex form impact socket then maybe a chrome socket, hex or bi-hex where a thinner sidewall is required with a ring key next. I was always taught to put the force on "towards" the shorter jaw of an open ender so in this picture I would be turning the fixing clockwise to tighten:
I have to say though that one of the most useful things you can use the open end of a combination spanner for is to increase leverage by looping another spanner through one of the jaws or, perhaps, applying a length of tubing:
You do need to be careful the spanner you are using to increase the force doesn't snap because you are using it across it's minor width but, in my experience, if the spanners are of good quality the open ender will usually round off the nut/bolt head before the "helper" spanner snaps - especially if you use a larger size spanner as the extra lever.
As you mention Stilsons I have great respect for that tool family and they - and their close "brothers" of the Footprint family - have often saved me from disaster. As you say their great advantage, over stuff like self locking pliers (Mole etc) is that the harder you pull on the handle the harder they grip the workpiece. The great downside of this is that they tend to mark up the workpiece and can leave quite deep teeth marks which subsequently tend to rust more quickly - I'm thinking of stuff like track rod end locking nuts which can be very tight indeed but you can't get a ring key etc on it because of the track rod itself. I've mentioned this before, but for those who missed it, years ago I came across this wee set of Stanley branded self locking wrenches on a special offer in somewhere like B&Q./Homebase/Wickes (I forget where exactly):
I have some excellent quality Stanley branded tools in my carpentry tool box but I don't think they stack up against the likes of Britool etc for mechanics tools, However they were on a good offer and I liked the idea of them as they seem to work on the same principle as a Stilson/Footprint but with flat driving faces rather than the aggressive teeth of the other tools. If you look here:
You can see that if I turn the handle so the nut is rotated in a clockwise direction, the jaws will tighten against the flats and the harder I apply force to the handle the tighter the tool grips the nut faces, just like the Stilson/Footprint. However it's driving faces are flat so no damage is done to the hex faces. It also has an inherent "ratcheting" ability which is very handy if you find the nut to be a bit too stiff on it's thread to spin by hand after the initial "lock" is broken. All you do is rotate the tool anticlockwise and the jaws open and jump back to the next set of flats ready for you to pull against it again. Another reason why I think it works so well is that it takes a 3 point contact with the nut - the Stilson/footprint grips on opposite sides of the nut - So it has very little tendency to crush the nut onto it's bolt/stud/track rod/whatever, whereas the Stilson/footprint, by gripping on opposite sides of the nut, tends to crush the nut to it's male thread thus tending to lock it up. Although I don't find a lot of use for them when at home - as I have a big choice of other tools - I do use the larger one quite a bit though, almost exclusively, for doing track rod end locking nuts and I always sling them in the boot (trunk) when going on longer journeys. With a size range from 8mm (5/16 for us oldies) to 24mm (15/16) they can cope with most of the stuff I might want to tackle at the roadside.
There was a conversation going in another thread recently about the newer bolt types - splined, Torx , etc - and it occurs to me that the "good old" hex head gave us the possibility of using a number of different tool forms - Sockets (in hex and bihex), open enders, ring keys and tools like these Stanley efforts (I'm sure there are others) to "attack" fixings, whereas the new forms require the specific and only tool so if you can't get access with it you're "shafted"