In my experience using LinkedIn ads, from a B2B perspective, I’ve found them to be the least effective and most expensive when marketing a product/service/promotion.
In saying that, I’ve had more success with Sponsored Content than anything else. I find InMail to be intrusive and in the same bracket as a cold sales email, which is now frowned upon in most markets. If I get one I tend to unsubscribe from that person. Text ads have brought very little value.
Of course, every business will be different, so your results may differ. It all comes down to the purpose of your campaign, the audience you’re going after and your budget.
For me, it’s all about giving things a try. Whenever I go to test a new platform for advertising I tend to allocate 3-4 months for testing and a set budget.