Most of my S&W revolvers, and that's all I own for handguns, include the IL - including my 642-2 pocket protector. I got accustomed to carrying it's bigger sibling, an L-frame 5-shot hammerless .44 Special - the 296, before I ever bought the 642. There was no question in my mind which would be my pocket .38 - my 2" 10, besides the obvious extra heft, would catch it's hammer regularly when I carried it in a coat pocket.
I doubt I'd remember to ever cover a hammer with a thumb to retrieve it - especially 'in the heat of battle'. The 637 is 'cute' - very much so, in a traditional vein. My last evil-bottom-feeders, a pair of AMT DAO 'Backups' in .45 ACP, were cleaned and traded-in on that 296 (and a 696 - both new closeouts) the same day I last shot them - almost seven years ago. One came right from my pocket - and had a ftf - cleared - then a stovepipe. The second one, all but unused, stovepiped. UMC ball ammo - I had polished their ramps too well, while the first one's ftf was pocket lint under the semi-exposed hammer. Sadly, the 296 and available pocket holsters proved too big to pocket. I had to belt carry it - infrequently. A Robert Mika pocket holster remedied that several years ago, but fit only 2/3 of my britches front pockets - the 642 came along and fits all of them.
Over half of my S&W revolvers have the IL - it is a non issue here. MIM parts are more consistent and quite strong - also not a problem here. I thought the then 'new' SS was a Godsend on the S&W 60. Yeah, I am an odd old geezer. I'm glad someone likes the 637 - it is 'cute' and needs a following.
Stainz