I use this Lowepro Toploader which fits my K20D+300mm DA, or K20D+180mm Macro, or even the Tamron SP 300mm/f2.8. It uses internal velcro supports so yu can fit more stuff at the bottom or use the outside pocket. Also has an All-Weather cover.

Except for the 500m So far it's the only one that doesn't have swathes (exaggerating) of dust inside the lens.

AFAIAA, neither lens is actually available as yet, despite what the stores show. They both have projected release dates in August, though I contacted Intro2020 last week and they still have no idea when it will ship. The Sigma has also been delayed at least once so far.

As to which is better - probably trying both out will only tell. I'm quite interested in the Tamron as it's a little shorter, lighter and has better magnification for macro. That and I'm coming to quite dislike Sigma lenses.

That said, DepressingReview recently tested the Canon version of the Tamron and say that they found significant problems with the focusing mechanism. However, since it's probably going to be different for the Pentax that may be moot.

The Sigma is also meant to have what they called HSM (SDM) whereas the Tamron will be a screw-drive for the Pentax.

Lastly, you could also consider the Pentax 50-135mm which they seem to pitch as the equivalent when you take into account the sensor crop (I don't, but it seems to be their thinking). This lens seems to have proven to be of very high quality and solid manufacture from what I have read. It also sports SDM and full weather sealing which neither of the other two will offer. Oh, and it is definitely available now and SRS have a cracking price for it at the moment. May be a bit to short for me, though.

They do seem to produce some great effects, but I tend to start feeling a bit queasy with some of the pictures I've seen after looking at them for a while

AFAIK, from frequent dialogue with Sigma UK, Sigma has no intention and never has in releasing this flash for Pentax P-TTL

Lovely. I also love that portrait of the lemur.

That's interesting. I use the O-ME53 and find it works very well for both macro and telephoto work.

That's lovely a crisp.

Because of the waist it's probably going to be a bee or a wasp. My guess would be a bee, perhaps an Andrena of some sort.

I've ordered from them in the past. So long as the item is in stock they seem to be just fine.