I don't see any sensible use for ETC50 or for the "bomblets".
For the ETC 50 I would agree.
However the SD-2 (AP) and the SD-4 (AT) along with the AB250 container give the Luftwaffe their historical tactical support mainstay.
Panzerblitz rockets are a late war development. The AB250 and AB500 container's gave the Luftwaffe the same capability of an area effect weapon to repel infantry and armour throughout the war.
While the Bf-109 was restricted to the AB250 container in 1942, IIRC, the FW190 series used both.
The ETC 500 rack was capable of loading 500kg bombs but the Bf-109 did not have the ground clearence to carry them safely. IIRC a variety of measures were tried to adopt the plane.
G2, G4, G6, G14, and K4 all had 20mm gondola.
Not claiming to be a Bf-109 expert but I do have some information for the "great 109K gondola debate":
Rüstzüstand kits changed designations during the Bf109K4 service life.
Bf-109K4/R4 - Heavy fighter with 2 underwing MG151/20 cannon.
Was changed in November 1944 to:
Bf-109K4/R5 - Heeavy fighter with 2 underwing Mg151/20 cannon.
Perhaps Butch2K can add to this.
All the best,
Crumpp