It has come to my attention that companies are having a really hard time getting Agile coaches to deliver value. Not surprising because Agile Coaches by definition, specialize in helping people through the emotional blockers to change. (Many Agile Coaches are essentially full time trainers, but let's put that aside and focus on the Coaches that are truly Coaches.)
Organizations don't know how to place a value on someone who works to get people past their emotional blockers. They can measure the team's success, but well maybe that team would be successful anyway, how can they really know? And why can't the high-priced coaches take on more teams? Clients always want to improve their ROI, right? It's kind of like hiring a resident social worker - if you watch the TV show "Billions", you'll see they have a social worker on staff. Coaches and social workers both tend to get offended when you try to boil their work down to a metric.
Enter the Agile Consultant. Less squishy than the Agile Coach, but adept at demonstrating value to clients on a regular basis. Consultants know and understand how to implement change in an organization, and how to make sure the client is getting what they pay for. Now, there are good consultants and bad consultants. Bad consultants just tell you what you already know, we're not going to talk about them here. Good consultants highlight the brutal facts and uncover lost value, so their clients can move to the next level.
So what do you need? Well you might need both. I recommend starting with some good consultants (I might know some) and tactically applying coaches where you have cultural issues. If your culture is in direct contradiction to the Agile Mindset, you might need some coaches, and this is something your consultant will work to assess.
At the end of the day, your consultant can tie a value to the work the coaches are doing. Without some good solid consulting, you may find your transformation rudderless.