I was hoping to use this as a long term solution for my LinkedIn outreach. However, after months of using the product, it hasn't lived up to my expectations.

Your network is your net worth and LinkedIn is today's business network. What will damage your network is:

Sending duplicate messages to connections
Missing messages because they aren't synced or are marked as read
Continuing to send messages when you have already replied manually

Unfortunately, Closely does all of these things are one point or another. I'm sure they are working on bugs like this, but my network is too valuable to be spammed so I'm going to go back to manual outreach as this works like a treat.

Weigh up the time you spend reaching out to people manually and building authentic connections vs the cost of annoying them or spamming them.