iPhone 5 issues with series 1 watch

Hi,

I'm considering buying an Apple Watch for my wife. She uses an iPhone 5. I know the watch is compatible with iPhone 5's. I'm wondering if it is fully compatible, or are some features of the watch disabled when using an older phone.

I can't say for certain but I'd like to think that the Watch should work in the same manner it does with new iPhone models. If I'm not mistaken, I had an iPhone 6 Plus, when I got my Watch two years ago, and it does now what it did then.

Thanks for the info.