Cheaper, not much. Not if you shop around and buy ammo in bulk. When Wally world sells 100/45 for $20 and the same amount of 9mm for $15 it is not that big a deal. Shop around and the cost of .45 ammo comes way down.
How does the Glock conceal easier? Are you comparing apples to oranges? There is not that much a size difference between a full size .45 and the 19 and almost no difference between a Compact .45 and the 19. There is not so much a difference as to make one easier to conceal than the other IMO and I have to handle both all day long.
Glock accessories cheaper? How so? Insight M3 $150 (GLock). Insight M2 $155 (HK). Not much of a difference. Anthing that will fit a Glock will also fit an HK if you spend $20 on the rail adapter that CDNN sells. They work great and don't cost an arm and a leg like the GGG and Sidearmor cost. Again, cost difference is insignificant if you do your homework.
Glock mags cheaper than a HK. Cannot argue that and won't even try.