Here is the honest review that you are looking for (kdrama expert here). I've watched both seasons. The first one had serious potential about an application that can tell you whom you like. Aside from the putting up the shield part, which doesn't make any sense whatsoever, the story was still somewhat believable and enjoyable.
Well, after waiting 2 long years for season 2, the plot just took a left turn , it's like nothing ever happened in season 1. It's like Jojo never cared about Sun-Oh and he's a complete stranger...when she's the one who was never honest with him...Still trying to wrap my head around that one...
As for the other guy (can't remember his name)...nothing wrong with him per say...yeah he was there for Jojo...but so was Sun-Ho...difference is that Jojo pushed Sun-Ho away without explanation and respect...
The real issue lies with Jojo. She was never honest with either man. Putting up shields, using the spear to validate her feelings towards the second guy...Get it together. Plus, she's acting like the victim by walking away on multiple occasions and choosing to withhold information/lying. It is quite difficult to sympathize with her (she's the lead so it's not so good).
The part that Sun-Oh will try to force himself to like his girlfriend is frankly pathetic and just doesn't make any sense for his character. He gets treated poorly by his ex...so he wants some type of comfort so he settles. Definitely not what the viewers want out of their protagonist.
Overall, the takeaway of love alarm (for both couples): one sided love can wear away the most unloving heart if you just keep on persisting?!?!
DON'T WASTE YOUR TIME, SKIP IT (good concept, good actors, people had hype and expectations for season 2, writers didn't deliver which is really unfortunate)