N135 is the canister version of Viht's 7.62X51mm NATO cartridge powder, developed specifically for the heavy-case 147gn FMJBT bulleted military version of the 308 Win to produce ca. 2,800 fps MV and NATO-spec gas system pressures within 20-22 inch barrel 1st Gen NATO rifles. So, it's very well suited to 150gn bullet match loads in the 308 (what I use it for these days). It was my favourite 223 Rem powder with 68-70s too back in the day.
IMO, it's too fast burning for the 6BR and Dasher with heavier bullets, but fine for lighter models as many posts say.
On burning rate, I'm very sceptical of its position in most tables/charts that often show it as similar to, or even slower burning than, Hodgdon VarGet and similar. IME, it's 'quicker' than H4895 or IMR-8208, and as some others have said I've also found it to be very prone to 'pressure spike' with small charge additions, especially if used in a combination that would better suit a 'slower burner'.
