What's the latest on good e-bike conversion kits?

I'm looking for something for my better half as she can't keep up with me on a single and there are some rides we'd like to do on singles rather than our tandem.

I think I'd prefer a front hub conversion as it seems like it would be easy to remove and re-install, but I'm open to ideas. I saw an article about Cytronex on Cycling Weekly, and it seems impressive, and the Bafang units seem OK.

Any experience anyone could share would be appreciated!