Using a border-bottom to achieve the look you’re describing is totally a valid preference. One potential advantage to the border-bottom technique is the way it can be used to make a link stand out. In fact, I use this link styling on my personal website for that reason [1].
(Note: when using a border-bottom, I’d recommend using a slightly larger line-height so that the line still seems associated with the text above it and not the text below it. This is one of the pitfalls described in the original Medium post [2].)
Unfortunately, aside from iOS 8, normal text-decoration underline links have the descender crossing problem.
I absolutely took this into consideration when designing SmartUnderline. SmartUnderline literally only applies itself to links with text-decoration underline, nothing else. It even tries to ensure other conditions which make the transformation favorable (display inline, solid background color, etc.).
Ultimately I think the before-and-after on the SmartUnderline website tells the best story [3]. No doubt one may appreciate other, very different link styles. (For example, just using a different text color to denote _link_ is a perfectly valid and commonly used technique.) But if you’re using text-decoration underline already, this just makes those links look better.
I think blogs, news articles and wikis are some of the primary examples of where these links look best. Anywhere where text is heavy and the links are _not_ the primary focus.
[2]: https://medium.com/designing-medium/crafting-link-underlines...