I saw a pair of warehouse deals Engage 10x42's come up for $110 a couple weeks ago, so I decided to jump on them. I have two pairs of the Legend M 8x42's which are my main birding binoculars. One lives in my house, the other in my car.
Comparing the 10x42 Engage's to the 8x42 Legend M's, I found the optics in the two pretty similar. I believe the general sentiment is that the Engage's are basically the Legend M's optics in a different form factor. I went back and forth for a while and found that the increase in size of the 10x42's seems barely perceptible. Meanwhile, the apparent FOV was noticeably smaller than the 8x42 Legend M. The eye relief seemed about as advertised (1mm less than the 8x42 Legend M, IIRC), but with glasses on I wasn't quite able to see the extreme edges of the image circle.
On the plus side, the Engage has a more compact form factor, and was perhaps just barely lighter. The focus was also better than at least one of my pairs of Legend M 8x42's which have always been stiff. Assuming the Engage 8X42's perform similarly to the Legend M's, I'd say the 8x42's are the ones to buy. Almost identical resolving power to the 10x42's and with a bigger image circle and more eye relief to boot.