The original H335 was a mil-surp powder. They ran out in the early 1990's and switched to a newly manufactured version, which was considerably faster.
A lot of .223 shooters have burned a lot of H335, because for quite a while it was one of the better ball powders available for the job. It metered well from a powder measure and usually shot quite accurately.
But the downsides have all been listed above: pretty temperature sensitive, especially in heat, and very dirty burning. It would carbon up a .223 bore so quickly that after 50 rounds you'd get the impression from looking at the muzzle the bore wasn't copper fouling. It was--but you couldn't see it due to the carbon! H335 was one of the main reasons pratrie dog shooters scrubbed out their bores in the field every 50 rounds or so!
All that said, if you're using H335 for deer hunting the powder fouling won't be a major problem. The temperature sensitivity might be, depending on the range of temps you typically hunt in.
