I use that style myself & I like it. It started innocently. I found some uncoated ones with sharper nose radius off Ebay or Ali specifically for aluminum. They cut like a dream & make a nice chip. My mainstay was CCMT 060204 which work perfectly fine, but at the time I could only find brand name inserts at like 8-12$ a pop or so from the tool catalogs. So now I just use my CCMT inventory on steel & DCMT on aluminum which is kind of silly but the way it worked out. Nowadays I think you can find either/or in any coating/radius/chipbreaker from offshore discount places so could probably pick one or the other as a standard.
DCMT is narrower & allows you to get into nooks & crannies of shoulder corners a bit easier which has come up for me occasionally. It has a bit more stick out so is maybe a bit weaker, but I don't think either of these are meant for heavy hogging. CCMT also matches a very complete set of boring bars so has more utility from that standpoint. Both styles only use 2 of their 4 corners although I have seen the odd commercial holder (or self made) that uses the odd corners which I believer are shaped the same. Some people say 3 cornered inserts are better from that standpoint, but again, how much for that type of insert & corresponding holder if they are not as common? My shanks are all 5/8" or close metric equivalent so I cant speak for big boy ones.
Things have evolved quite a bit the past 5 years. When you can buy a toolholder from China with free shipping for the price of a single insert from NAm supplier, it swings the decision. Some people say offshore tool holders are crap which some may well be. I've cut some of mine up or otherwise modified them & I think they must be reasonably tough stuff like 4140. So if I'm not pushing them hard or in production, I think they are decent value. Some of the screws can be a bit cheesy, others are fine, it really varies. OTOH some of the 'big name' tool holders have slightly different (proprietary?) insert screws or clamps which makes them PITA to replace.
