I agree with the ups above - but it really depends on what you want to achieve with it - personally ive had a couple of these and just changed the trigger, QEV, added a clamping feedneck and on/off drop.
If you want to add a coloured shell then cool, but the basics above will make a good cheap marker a lot better without breaking the bank.
Ive just added all the above (except the QEV so far) to a project ion for less than £40. Add an ultralight and its a nice little marker.
You dont need to go crazy on these things as it prob wont be worth it when you sell it in the future - just up the basics in my opinion as above. These shoot pretty good for a cheapy gun out of the box.