I felt a similar vibe on both shows. Both have very light stories - not too serious, not too complicated, not too romantic. Some may find these shows boring but I must say that they are both realistic in depicting real life high school romance.
Both have a really similar atmosphere even tho I consider Just Because much better in every detail.
Both have various relationships.
Both have a really slow pacing.
Just Because has an overall better draw and animation, so if you watched Konbini Kareshi and you liked it, you should be ok with this one.
If you watched Just Because first, you should watch KK only if you... I don't know it is not that good, but that doesn't mean they are not pretty similar series.
The length, pacing and overall style are obviously different, but the setting (highschool life, several couples) and general vibe (strong focus on romance, long-time crushes, pending confessions) seem quite similar to me.
Both anime focus on a different pairs that come closer over time and their struggle to come clear with their feelings.
Both anime also have the same strength that the unusual pairings are the more interesting ones while the more normal ones tend to be a bit on the more basic side.
In general you could say if you like one you will probably like the other, because both anime have a very similar feel to it, but Konbini is definitely the weaker one of the two.
Each series focuses on different couples and how their love story and confessions play out. Itsudatte Bokura no Koi wa 10 cm Datta is more focused on one main couple from the original movie, but this couple is extremely similar to the main couple from Konbini Kareshi. They both take place in a high school setting and a very similar basic cast of characters. If you enjoyed one I would recommend the other for a similar story and overall feeling.