Umm..in my experience the exact opposite is true. fast films lose speed more rapidly than slower films. I have 100 ISO film that expired in 1964 that still seems as good as new.
Shoot 'em! Kentmere 400 and 100 are fine films. My knew favorite high-speed combination is k400 at 800 in diafine. Minimal grain, sharp, scans very well.
I've decided to try the Kentmere 400 in my new Diana Mini. As it's a plastic camera like the Holga, I am expecting similar results as the Holga, but if the images otherwise come out decent, I'll definitely keep buying it.
I used Kentmere 100 and 400 films. They are good general purpose film, nothing special with them. They are different form FP4+ and HP5+.
It is not true that they are very grainy. Quite normal B/W films.
I agree; I usually use Ilford films, but have occasionally used Kentmere, processed according to the manufacturer's recommendations, and, as you say, quite normal, reliable quality, general purpose films. I would prefer to use them (or Ilford) for consistency, compared with cheap unknown products.