So I've noticed that SH autocancel aerials always puts Bowser into his hard landing, the same goes with side b, I did a bit of dabbling around with both custom versions, I can see why everyone likes the dash grab, but I feel like a few were a little quick to judge the dash slash, it covers more distance, has even less lag than the other klaws when you land it, and while it may not beat counters and shields or give us the Bowsercide option, or K.O very well if at all like the default version. It does give Bowser a pretty strong aggro and approach game, and it looks like he can get some combos off of it and it can still be used to transition into an offstage situation. I feel like it also help's Bowser's throw game since You may very well get to follow up from a down throw this way.
From the right range, it it'll klank projectiles, and if you time it perfectly then you can klank the projectile right next to them, leaving them stuck in cooldown while you're in thier face. Also, You can use if for off stage edgeguarding either the hit itself or just the mobility to go further offstage before using it again to return. Finally, you'll never have to worry about having to be super careful in it's use because of being behind a stock.
I am in no way saying that this is the best version, or that everyone should be using it, but I don't think it deserves to be ignored either. The fast fortress also seems pretty great, it's the only version I've tried so far but I actually like it, it's pretty active, hitting through most of it's animation, and it seems decently safe as long as you aren't predictable. If anyone gives you the slightest opening then you will very likely be able to escape with this version. Offstage as a recovery it doesn't go as high but the vertical range drop didn't seem too drastic to me, It's definately still useable as a recovery. It seems like you can use it's active frames and speed to cover multiple evasive options pretty safely, I feel like you can run up and use it, pause for just a moment then press forward or back to roll away, if they shield, then you have a good chance to escape before they can grab or shield drop to punish you, if they spotdodge, you waited in place for a bit, so they'll get meatied, and if they roll then all you need to do is read the direction and you might be able to hit them out of it. If it hits, the knockback combined with your movement is pretty generous so getting punished on hit might not be a major concern with this version. It can still be used reliably OOS as well though it does appear to be just a tad bit slower. However, it's a free escape when it hits OOS, which is good, it puts a lot of space between you and the opponent, which could give you time to recover if they had the momentum for a while.
Then there's Turbulent Bomb, this also seems like a pretty safe move because of the windbox, it pushes quite far, and is pretty big, so if they are trying to grab or smash you when you land then they'll get pushed away and you'll probably be completely safe. It doesn't seem to be as great for damage or K.O. However, it's pretty amazing as an edgeguarding tool. If anyone fails to snap the ledge with Up B when the windbox comes out they are probably done. Either they'll be blown too far away to make it, or you might push them in a way that would set up for a free hit. So I would probably use this as a surprise landing tool and for edge guarding mostly.
I'll be honest, at first I didn't see myself using any of Bowser's customs but after taking a look at a few of them for myself, I may end up using them after all, despite how straightforward they are, they are still pretty good.