So here you go, this is my honest opinion about both for what it’s worth.
If you want a good, long lasting, no maintenance, cheap pedal because you are on a budget get the Shimano PD 520. If you ride with this pedal in good conditions you will have no problems. If you are riding in poor conditions, then take them off and put some platforms on because you won’t be clipping in anyway. If you want a better pedal, then buy a Crank Bros pedal and you will use this pedal all year long. Maybe that’s why they will need maintenance because you will be getting more mud and salt in the bearings and bushings, which ever you choose. If you don’t agree with any of this then…well I don’t care. Go ride your bike! Captain Ahab.
11/24/2016 update: Well it's been awhile since I wrote this blog and I have some updates to add. My road bike's Egg Beater 3's failed at about 2500 miles I would guess; most likely more. The nut came loose and the pedal came off the spindle. I was able to ride to a bike shop in route and borrow a socket and put it back on and finish the ride. When I got home I took them apart, cleaned and lubed them, and put them back together and have been riding on them ever since. My main mountain bike Egg Beater 3's failed at about 500 miles I would guess. These took some nasty hits in crashes, had mud abuse, and took a lot of high speed snags on rocks and roots. The bearing exploded into a million pieces in the first two miles of a 12 mile fairly technical (for me) trail. I had to ride by clipping into the broken pedal and sliding it on the spindle and holding foot pressure inward towards the bike. It was uncomfortable, but manageable. I emailed Crank Bros and shipped them to them using their process, which they paid for. I neglected to save a lot of my receipts, which they really want for warranty, but I told them how many pedals I purchased and they helped me out. They serviced the pedals and sent them back to me for free! They were very pleasant to work with. I haven't got to try the serviced pedals out yet, but when I do I will come back and tell you all how they worked. Those used Egg Beater 2's I have been running on my CX bike for gravel have now logged many dusty miles and are still working flawlessly. I cleaned and lubed them once I believe. So if you are going to buy Egg Beaters, maybe save some money and buy the Egg Beater 2's, and if you buy 3's, then be prepared to service them more often, save your receipt, and trust Crank Bros to fix them if they break; from what I have seen, they will. Here is a picture of my serviced pedals. - Ahab.