The Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight mounts to picatinny accessory rails. The XD 4" Service model may not have enough rail to fit the Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight. I recommend using the Streamlight model at the link below.
https://www.opticsplanet.com/streamlight-tlr-8-weapon-light.html
The Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight is compatible with picatinny and Glock style rails. So yes the Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight will mount to a Glock 41 Gen 4.
The Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser will not fit a Glock 29. The model listed below will fit a Glock 29.
https://www.opticsplanet.com/streamlight-tlr-8-a.html
Yes. The Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight will fit the Glock 40 using the "GL" key provided with the flashlight.
Yes. The Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight will fit the Glock 19 using the "GL" key provided with the flashlight.
The pressure pad for the Streamlight TLR-2 Tactical Weapon Flashlight w/ Laser Sight is not necessary/required to use the light. It has toggle switches like a standard TLR-2 or TLR-1 on the back of the light to activate it.
The flashlight is 300 lumens. 650-660nm red laser, Laser provides long-range targeting. Yes, they make it with a green laser as well: SQ-FLW-69265-1
Yes this will fit those handgun models.
This light will be too big for that model pistol.
The main difference is with the features and accessories.