What are key metrics and potential blind spots in UA Reporting / Dashboards?

This is a great question!

This is what I consider to be a "minimum viable report" for mobile UA (each of these would be presented by ad set / campaign / channel, as available):

• Some selection of DX ROAS, given the date range being considered (eg. Day 1, 3, 7 if I'm looking at the last 10 days of data);
• Predicted DX ROAS for whatever timeline I am buying against (eg. Day 180);
• A time series of whatever optimization metric is being acquired against (eg. Cost per Payer, Cost per DX Retained, Cost per Install);
• Spend / install metrics (if I have a report with a filter console, I want to be able to very quickly toggle cost / installs metrics between some traffic filter and the topline, overall numbers);
• I like to see the composition of DNU over time -- the % of DNU represented by the various channels. If there's a change in composition, that change can manifest in other metrics (which is why it's important to not look at topline metrics in isolation in the first place);
• I like to see ROAS curves for monthly cohorts going back some months (eg. 6) to know if ROAS is degrading over time. These are all indexed from Day 0 so they can be easily compared along the X axis 

1. Mine would be (per ad set/campaign)

- blended return/active ROAS at various points (3d, 7d, 14d, but various a lot depending on the title and UA strategy)

- Outbound CTR

- CPM

- CPI

- IR

- CPP

- # Unique payers

2. If running worldwide UA, often various country splits just muddle the picture.

3. For me that was tracking daily blended return for every single ad set (see below) -- it improved the agility of decision making.

4. Depending on the selection of metrics, I've seen people killing good campaigns and dragging the bad campaigns for longer. The most commonly overlooked metric is the number of unque payers, when one random whale "feeds" the losing campaign for weeks.

I've been using a very simple template to track daily ROAS by manual entry from the FB Ads Manager: https://docs.google.com/spreadsheets/d/1KbRzSemRn5ROYsl1jEfiodHmZI73IqF40woa2Es4tnI/edit#gid=1292744512

The template tracks blended return/active ROAS at various days which different depending on your title. I used it daily to assess the state of my campaigns and to make changes, which are also logged in this file, so you can see all the historical changes in there.

I know this might not be enough for everyone, but especially if your UA strategy is ROAS-centric and you know your KPIs, I found it really useful as a reporting and decision making tool. Ideally this one would be coupled with some of the more visual tools that ingest data directly from your accounts via API to give's you a bird's eye view on various metrics.