I like FETs as much as the next engineer but if you're going to write about them, try to not make things worse.
In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT.
I was helping a high school student with a transistor project and he was complaining that "half the FETs he bought were 'bad'". And they weren't really bad, but they were destroyed. They were destroyed because, like our author, the student had no understanding of how the FET worked and so didn't realize that when you exceed the maximum Gate voltage on a FET it generally causes a current to "jump the gap" to the source and that permanently breaks it. What is even more, since the gate is essentially a capacitor, you can just touch the gate with your finger and pass enough charge (without feeling a shock or anything) to greatly exceed the gate voltage. Pick up the FET without being grounded and "boom!" dead FET.
Now there is almost no way to generate enough current by touching a Bipolar transistor to kill it, and so they continue to work for a long time while plugging them in and out of breadboards.
Do they dissipate more power? Absolutely. Are they difficult to run in parallel? Sure. But they are pretty robust parts. Sort of like the difference between alkaline batteries and LiON rechargeable batteries. Sure the latter are a "better" choice, you can recharge them after all, but if you use them wrong they catch on fire, if you short an alkaline battery it gets hot but doesn't go ballistic on you.
So those "antique" parts are generally very cost effective, very robust, and easy to get. So they make excellent tools to teach you the basics. Do you want to stay with them as you get more advanced? Probably not, but you're probably not skiing on the same skis you learned on either.
/endrant