My 2 cents worth:
For dedicated clamping like the table or spiral milling attachment or vise i roll my own.....
Turn a stud with a head that is just a little thinner than the height of the lower part of your "T" slot
OD to be large enough to mill a square that will fit the width of your "T"....
Can make the grip length exactly what you need...Turn the step with a minimum radius so as not to foul the inside corner of the slot.....
I use pre hard 4142 or ETD 150 for these....very strong..no failures in years of use....
I use flanged nuts and hardened washers (available from McMaster Carr)....
As to regular clamping...For my use i prefer the "T" nut and stud setup. On repair work there are times where the ability to feed a stud through a hole or pocket is to advantage over lifting the [part up and tryiong to skewer
a stud through...
Also not a big fan of the forged type nuts on those one piece studs....many have large fillets at the corner of the "T" that can screw up your "T" slots...
For my NC Deckels i use standard "Bridgeport" style clamping kits (good quality) and narrow the "T" nuts slightly to fit the slots....Can be done using carbide tooling and assures a good inside corner.
Gives the advantage of having standard (US) 1'2-13 hardware (studs, coupling nuts and clamp nuts)....Which also fit the Kondia knee mill in the shop.
Cheers Ross