I promise I'm not "cyber stalking" - just looking over your previous posts (since this Forum is still small right now, and the number of past-posts reasonable) to help me compose a more directed post that will hopefully help you in terms of your first training class.
To answer this question above, well, "it depends."
There are pocket magazine-carry options that can be *really* fast to reload from - the same as with an OWB setup, assuming that the pocket itself amenable to the task, that it is cut/constructed in a way that makes retrieval of the "held" magazine from it not overly awkward.
Examples?
Items like the SnagMag (https://www.snagmag.com/) and NeoMag (https://theneomag.com/) replicate the way that a folding pocket-knife or flashlight resides in one's pants/shorts pocket, and makes retrieval of the staged magazine a motion that is virtually identical to that used to retrieve a magazine from a "traditional" belt-mounted magazine holder. I favor the latter, mainly because I have seen the SnagMag fail to "snag" and thus come out of the pocket with the reload magazine (the shooter encountered this for the very first time at class, and couldn't figure out what to do: the remedy is actually quite simple - just strike or snag the SnagMag device off the withdrawn mag, and then reload the gun as-normal), but also because I've seen just how quickly a NeoMag exchange can be:
^ Graig, the man behind NeoMag (and someone who I actually routinely see at local classes here in NE-Ohio), demonstrates live-fire starting at around the 3:15 mark.
Devices like the DeSantis MagPacker also work well. They will put the magazine completely inside your pocket, so access will be a bit slower (and you'll want to make sure that your pocket's opening is not so tight that you won't be able to get your hand sufficiently inside it to get the mag out), but aside from this potential concern, the Mag-Packer will absolutely hold your magazine in the proper orientation to facilitate the reload.
[ My use of the Mag-Packer is a bit different - I use it in polite company, to fully bury my pocket-knife inside my pants pocket, while still maintaining the correct index/orientation for the draw. ]
IWB, overall, I find to really not be that different from OWB - the only big exception coming from deeper-concealment options that drop the magazine significantly more below the beltline than how a normal OWB setup would ride. For example, as I've shown in another thread, my EDC setup for a spare magazine comes from the Comp-Tac Concealment Magazine Pouch - https://comp-tac.com/magazine-concealment-pouch-iwb-mag-pouch-comp-tac/ . With this, to enhance concealment, I have my magzine shoved so low in my beltline that only the base-pad portion sticks out above, and as a result, this does take me an extra beat to reload from (my spontaneous reload from OWB is typically in the mid-1-second range, the use of my IWB setup consistently adds close to a full second to this figure). But here, since I'm more worried about fully concealing the magazine, I'm OK with the compromise.
