MB05s are just like L96 clones. They aren't the best but they are decent for beginners. If you upgrade one just like a clone l96 it will perform the same. But, they are kinda junk rifles just like all the other spring sniper rifle clones out there, I don't think any of us would recommend one.
But if you do want an MBO5...
Well all the MB05 type rifles are just re-brands of the Well MB05. The MB05 is just a clone l96 with a fancy stock. So, it doesn't matter which one you get, just find the best deal.
Most clone guns are hit or miss anyway. Lemons are not as common as you think, but they do occur at a frequency that will make you scared to buy one.
The only thing you need to do to make the gun last with the utg power upgrade kit, if you choose to get it, is to reinforce the trigger box with some epoxy in key places. I don't have the link to the thread but it's on the forum somewhere ( Edit: I found it
http://www.airsoftsniperforum.com/phpBB/phpBB3/viewtopic.php?t=1246 go to the shredders link in one of the posts it'll have a picture in it that shows what to reinforce just scroll down until you find it) . The kit is not the best, but it is decent if you grease the parts enough and make sure you get good compression. You should get 530+plus out of the upgrade. You can also do the diy upgrades just follow the ones for l96 clones and adapt the stock fixes to your mbo5.
But that's a whole other story.
And don't get a JG bar-10 they are even worse.