3 needed to calculate an average
Both series (well, in Tenshi no Okurimono it's just the titular oneshot) revolve around a guy who meets his future daughter. The girl tries to help the guy meet (and become a couple with) his future wife. In short, the plot is similar. On the other hand the style of those series is very different. Nonetheless if you found the story interesting in one of them, you should check the other one too.
The titular story from Tenshi no Okurimono and Mahou no Iroha! have a similar plot. Both revolve around a little girl from the future who tries to get get her (not yet married) parents to get together. Mahou no Iroha! is more comedic and has some bits of fanservice, Tenshi no Okurimono is just a oneshot, but doesn't feature any fanservice.