Really a cool novelty airgun, good for requiting PB types to airguns, all the ones that look the same ( 909 , senica , other even tho different companies) are basically the same internals.
The 909 was the first pre-charged I knew of that you could get any ca;. barrel from .177 to .50.
As long as you have a spanner wrench & rubber mallet a barrel swap can be done in a minute & 1/2 , not that you'd want to rush that much while having fun. My Wife is NOT mechanical but could strip & reassemble one of these rifle in 20 minutes, ad another 5 minutes on even a grind wheel to slot the sides of the front valve body - spares are available OEM and after market-. .
Now that was before all the great looking valve kit's came out, personally I would still do my own except I would purchase a valve stem somewhere but if not wanting to do the "machining" you come out ahead many ways doing it yourself, money, and the enjoyment of DIY.
A personal note ( j IMO ) "I" dont like touching the triggers on those and they arent TOO good - unless your a common BP shooters, might not seem so bad then, still it is easy to make it unsafe and might be best if a pro did that work except a sping chnage.
John