I would think 42008 is a good start into pneumatics. Good value for money. The only thing that stopped me from buying it is the colour. If only they made it Blue or Orange...

Once you go down the Technic path, there is no turning back! First you buy the 42009, then after that 8110, then followed by 8043 motorized excavator, 8275 motorized bulldozer, 8258 crane truck, 8880 supercar, 8448 super street sensation, 8868 air-tech claw rig etc. I know since I started with crane truck and then every year buy the flagship technic set (last year was an exception though, skipped the crawler). 


I do not own the crawler, but Technic models are definitely not meant to be played outdoors. There's a video from Technic-bricks where they drove their crawler on the beach but they warn people against doing so. This is because dirt/sand might enter into the gearing and grind the gears out. The gears are all plastic and not meant for heavy usage. 

If you really do need to buy a Technic set each year, then better buy the flagship technic set. The smaller ones no shiok lah.
8110 is much more complex and larger than 42008 when it comes to pneumatics. Not only that but 8110 is also much larger and has a much higher piece count. Prior to the Mobile crane Mk2 it was the largest technic set at 2048 pieces. Then it has 4 wheel drive and suspension, motorized winch and turnable, 4 super big wheels and rims, comes with Mercedes logo and in cool orange livery.


For pnuematic functions you control 3 different functions via the 3 switches- the claw, the top part of the arm and bottom part of the arm. Compared to 42008 you only control the wheel holder (if that is what it is called)


The 8110 is the 2nd model to have a compressor after its grandfather 8868 Air-tech claw rig. The 8868 comes from the 90s so you can see that the construction method is different.


Recycling my old photo for this post. I really need retake all of them again and see all of them line up in a row. I wonder how big is the 42009 compared to my other behemoths like the 8110 or 8258.