Reasons for Rear Ejection
1. Delicate rear fin structure, so you want it to come down nose first, so the initial impact between rocket and asphalt is the nose cone.
2. Boost Glider models that use a central "pop pod". A big advantage here is you can put some extra mass/weight in the forward edge of the pod that will eject with the pod. This gives you better stability on boost, but both takes that weight OFF in glide AND moves CG back on glide. Good example of this is the Apogee SR-71 DarkBird
3. Sometimes it just fits with the concept of the model, example is the Pyramid mentioned above, also the Uranus Explorer
https://www.rocketreviews.com/umm-me-uranus-explorer-2-scratch-by-tom-markel.html
there may be some other reasons I haven't thought of.
Rear ejection is definitely more complicated and less reliable, as the central tube has to extend forward of the recovery device (has to push everything BACK) and therefore you have MUCH less space for your streamer or chute. We are talking really tight. Advantage (and it is a minor advantage) is you don't need wadding. The forward SLIDING centering rings (fixed to the pod, slide relative to rocket) will prevent exhaust from hitting your recovery device.
If you want to use this method just for it's "cool factor", recommend you use a LARGE body tube for your rocket (say at least BT-60 for a BT-20 motor mount), and make it a fairly LONG rocket, don't try this with short and stubby. If you read the Uranus Explorer review above, you will understand how I know this.
I also recommend if you have the space for it that you use separate recovery devices for the pop pod and the main rocket. That will take the weight of the pod and engine off the main rocket on descent, which I think is an advantage. For an 18 mm engine pop pod, that can recovery easily on just a streamer.
When you pack it for launch, the pop pod should be so loose it almost slides out on its own. If it seems tight at all, don't launch. High chance the pod won't eject (and then your rocket will DEFINITELY come down nose first!)
Good luck and straight trails
And soft Landings!!!