I find the Junior quite different from the Runt. We often see the Junior compared to the NOVA, probably due to the lid for secure and close the brick, but for me the NOVA looks more like a Runt than a Junior. In fact, the NOVA draw resistance with standard dimples stem (so a smaller than a Runt) is quite similar to that of the Runt with a smooth longer mouthpiece in terms of cooling, I find them quite similar on this point and the size of the Runt is much closer to the NOVA than to the Junior, which is much smaller in this respect. The junior is actually the smallest brick I own (sorry it's night here and I can't take a picture). The NOVA is a damn good mix between a Runt and a Junior, it's a fantastic brick! It's simply a Runt in a Junior design (I find easy one-handed handling)
You will probably have to adapt your drawing technique in comparison with the Runt, as the distance is shorter and the steam is hotter. But I'd say the draws are faster because there's less distance (the low height probably has something to do with it too).
I haven't had much experience with the Junior so I won't be able to help you much with the mouthpiece because I'm quite sensitive to Padauk wood, so I use my Junior exclusively on a water filter. I find it excels in WPA (you can leave the top part on the glass and easily remove the bowl).
I prefer the NOVA to the Junior and I prefer the Runt to the NOVA, if it makes sense (but it's a personal opinion).
It seems to me that you already own a NOVA? so I don't think it will be of any use to you? why not use the NOVA for hiking? If you're looking for something truly portable, you should take a look at Retrosteam Cuban, which is simply fantastic and perhaps less expensive than a Junior, depending on the type of wood you want