Mech pencils are great, of course you CAN press down (but you dont need to), but you need to control the amount of lead you push out, simply press down on the cap, and then push back in excess lead, when you release the cap the lead will shoot back in leaving you just enough and you can do harder shades. it's better to have a metal nipped Mech pencil, even with a metal body, but those can cost more, im fortunate to have gained a couple thought life. However the ones that are entirely plastic and supposed to be disposable are equally as useful. that said there are a number of differnt brands of leads and you have to find the right one, i dont recall which i use and have used for the last five years but you can get all the shades you need.
Whats more my mothers a jewellry designer and crafts woman and sinc i gave her my Mech she can do much more intricate designs....logical considering Mechs are standard amongst most people who do architextural drawings etc. i can draw very complex images on very small paper, all the drawings ive posted were illustrated on a small part of A4, wood pencils just dont beat it....plus it's more enviromentally freindly and less wasteful. but each to their own.

well i wouldnt ink illustrations with a brush, it's too time consuming, i save my india for mass shading.