If you're upgrading from the iPhone 7, the iPhone SE probably won't feel like too much of a difference other than its faster performance and Portrait Mode camera. You'll have to decide if those two improvements (along with the additional storage) are worth a $400 upgrade.
If you have an iPhone 7 that's starting to feel a bit slow, are willing to spend a bit more, and don't necessarily care about having the latest iPhone, the $600 iPhone XR might be also be worth considering.
It has an older processor compared to the SE (it runs on Apple's A12 Bionic instead of the A13 Bionic) that should still feel faster compared to the iPhone 7, offers a larger 6.1-inch borderless screen compared to the 4.7-inch iPhone SE, has Face ID, and longer battery life.