Regardless of the type of speed loader or speed strip you use, none are effective if you don't practice. I practice w/ my Bianchi speed strips w/ dummy rounds several times a week. Perfect practice makes perfect. FWIW
When I CCW carry my 638 I have 2 Tuff Products Speed Strips in special pockets in my jacket for winter. I also still have my Bianchi #22 belt pouch when I am not wearing a jacket. I have probably had that pouch for 35 or so years.
When I shoot BUG matches I use Safariland Comp I loaders for my reloads.
As someone else mentioned probably on the second page, they can be a pain to load up. One of mine does not load as easily as the others.
My 437 had problems ejecting the casings but after shooting a couple hundred more rounds through it, I never had that problem since.
I use HKS speed loaders in both my 437 and model 19..... those are the same type of speed loaders that my mom uses for her duty gun for years and she never had a problem with it so I feel good about using it for my guns.