While both of them are truly poor quality guns, The better one in this case would be the mongoose just because it has eyes, which will cut down on the amount of paint you will chop. I would recommend however that you look at the Azodin Kaos which is of much better general quality than sypder or diablo guns.
It depends on what you are going to use it for... If you are going to play more speedball, get the sonix... If you are going to play more woodsball, get the MR1.
The sonix, because it has an actual hand grip.
no. only if the title of your paintball marker says "electra"
It is not recommended you do this for safety reasons.
Spyder Sonix can use any Co2 or HPA tank
Absolutely!
Buy a Spyder E-trigger.
Most likely the striker o-ring is broken or needs to be lubricated. It could also be that the sear is work, or the mainspring could be worn. Take it to a local paintball store to have it looked at.
On the bolt cap there is a small twistable screw. Put an Allen wrench in there and it will go up or down. NOt sure witch way does what though.
Disconnect the air source, pull up on the bolt, and slide it out of the back.
They are the same gun with slight variations. The sonix has a hand grip, clamping feedneck and different ASA hose and the victor is slightly cheaper because it doesn't have those things. Neither of these guns are very reliable or what could be considered "good" I would look into the Azodin Kaos before buying either one of these.
depends on your budget and what you are looking to do with it, a great beginning setup can be something like a spyder sonix at around $120 with a $50 eye force hopper and a co2 tank or something for a pro can be something like a $1200 DM-10 with a $150 rotor and a $150 tank along with a lot of other paintball goodies