I had an AT-440mla in my Orbit for the year and a half I used it and loved it.
Setting up a cart the first time can be intimidating. I'm sure you can find a guide on YouTube to help. But with a pair of tweezers, a well-lit table, a stylus force gauge, and some patience, it's certainly doable.
Here's a written guide to get you started: if your cartridge has a stylus guard, put it on. Use the tweezers (preferably a pair that isn't too sharp-edged) to detach the 4 colored connectors from the pins on the back of the cartridge, taking care to only grip the rubber covers over the connector, not the connector wire itself. Then remove the screws holding the cartridge to the arm. Mount the new cartridge on the arm with the screws that came with it. Don't tighten them all the way yet, just enough to where you can slide the cartridge back and forth and it will mostly stay in place. Then VERY CAREFULLY use the tweezers to attach the pins to the back of the cartridge. Some cartridges have little colored dots to indicate which connector goes to which pin, but if your new cartridge doesn't, the manual should tell you the correct connections.
Next, print off the "stupid protractor" from this page:
http://www.vinylengine.com/cartridge-alignment-protractors.shtml
Be sure your printer doesn't scale the page and that you print it at full-size. Glue it to a manila folder or something stiffer than a sheet of paper. Punch holes through the two black dots, choose one, and put it on the platter spindle. Move the platter to where the grid closest to whichever hole you're using is under the cartridge. Align the cartridge so that the whole thing is square to the grid, then adjust the whole cartridge backward and forward until it hits the crossed lines in the middle of the grid dead on. Once it's dead on for the first grid, tighten the screws a bit more. You'll still need to be able to move the cartridge, but you're making minor adjustments now. Move the arm so that the needle is over the other grid (you'll need to turn the platter some) and repeat the alignment process. Go back and forth between those two grids until you have the alignment as close to spot on as possible for both grids at the same time (i.e. when you put the stylus down on the center of one grid, then move it to the other grid, it should be centered on the cross in the center for both grids).
Once you've got everything lined up, pull out your stylus force gauge and put it on the platter. I use the Shure SFG-2. It works pretty well, though the Orbit arm is so light, you need to place the arm in the gauge's groove a few times to make sure you're getting an accurate reading. Adjust the weight back or forth on the tonearm as necessary, then take another reading, repeating until it's at the correct weight. Don't adjust the weight with the arm on the gauge. Only adjust it with the arm in the tonearm rest. If you don't have enough weight to get the force correct, try putting a gob of blu-tac on the back of the weight. The cartridge manual should tell you what tracking force is ideal for whichever cartridge you have.
Once you've got the alignment and tracking force set— plug everything back in and start playing records!
