"Alex Alex" Glock 44 15-Round Magazine

Preface
This is a DIY project to convert an OEM Glock 44 10-round magazine to 15 rounds. The conversion may be simplified using 3D-printed and other replacement parts.
Background
This 15-round Glock 44 magazine (pictured at the top of this thread) was based on a concept developed by Alex Alex (AA),
You must start by removing the load assist tabs. You can separate them by getting up under one tab using a standard screwdriver and gently prying them apart. The load assist tabs won't be permanently damaged in the process.
Cut-Down Follower
You get +2 rounds by cutting down the follower ...

(Left: Cut-Down OEM Follower; Right: Original OEM Follower; Both with OEM Spring)
Here's a simple jig to cut the follower,

Note: The screws hold the follower such that the cut is perpendicular to the edge of the jig.
A short length of 1/8" flat aluminum bar serves as a guide in cutting a new slot on both sides of the follower to hold the spring,

New notches are cut by hand using an X-Acto knife and the edges are rounded using a file,

Magazine Extension
The "Alex Alex" Glock 44 15-round magazine leverages an OEM Glock +2 magazine extension (SP07151) and, optionally, an OEM Glock magazine extension insert (SP07165).

Alternatively, you can use a $3 Chinese knock-off (AliExpress / Magorui) +2 magazine extension and insert. You can also purchase the insert on eBay for $2 (seller lxranes9).
The notches of both the OEM Glock +2 magazine extension and the AliExpress / Magorui +2 magazine extension don't completely slip over the tabs on either side of the Glock 44 magazine. You should widen the notches by a millimeter or so to ensure the magazine extension locks in place (kudos to ViperR),

Note: You don't use the flat insert that comes with the OEM Glock 44 magazine.
You get +3 rounds by incorporating +2 magazine extension. The extension must be "padded" (made more narrow) to keep the spring from twisting / contorting. There are three approaches to padding the magazine extension ...
Approach #1 In his video, AA directly padded the +2 magazine extension using a hot glue gun.
Approach #2 The author opted to pad the magazine extension insert (OEM SP07165, AliExpress / Magorui knock-off or eBay 3D-printed insert). The insert must first be cut down (remove the portion of the insert highlighted in gray),

Pack the the cut-down insert with epoxy putty (e.g., J-B-Weld PlasticWeld Epoxy Putty), then press the insert into (and remove the insert from) the magazine extension. This ensures the diagonal slots on either side of the insert are clear of epoxy putty that may have "seeped" through. Allow the epoxy putty to dry. A slot is then drilled out using a drill press and a 1/4" drill bit. A metal file is used to square all four sides. A palm sander gives the padded insert a more finished look. And finally, a splash of flat black spray paint.

Here's a picture of padded inserts in the +2 magazine extensions,

Note: Some of these +2 magazine extensions and inserts were OEM. Some were AliExpress / Magorui knock-offs. They are indistinguishable. The more square inserts are from eBay. All of the inserts were fashioned by hand and hence the slight variations.
This approach was intended to serve as a prototype for a 3D-printed padded insert.
Approach #3 Alex Alex has developed a 3D-printed custom insert that can be found on Thingiverse,

A number of community members have observed that the spring tends to catch on the cutouts of the Alex Alex 3D-printed insert. This is especially true of the lighter-gauge Walther spring (refer to Spring below).
A few observations from G8V8 ...
With Approach #2, the floor of the insert would normally add thickness to the magazine extension. Drilling out the floor frees up this space. With all three approaches, the spring sits directly on the floor of the magazine extension allowing for the spring to be less compressed. This added space is beneficial in inserting a fully-loaded 15-round magazine into the Glock 44 frame with the slide closed. The added room allows the top round to compress.
Replacement Spring
With the cut-down follower and +2 magazine extension, you need a longer spring to ensure the slide locks back following the last round. There are two options. One option is to stretch the OEM spring. However, there is a concern that the OEM spring will return to its original length after repeated use. The other option involves using a replacement spring.
Several community members are trialing the Walther PPQ 22 15+1 Replacement Magazine Spring from Taylor Tactical Supply,

(Walther PPQ 22 15+1 Magazine Spring)
Refer to Replacement Springs for more information.
Here's a picture of cut-down followers paired with the Walther 15+1 spring,

Conclusions
We are awaiting more range time in order to draw any final conclusions, however, the "Alex Alex" Glock 44 15-round magazine has shown tremendous promise in preliminary testing.