I work for a water company and we are currently working on our winter hydrant inspections. I have created an awesome map in AGOL (thank you ESRI!) to log and store all of our maintenance duties performed at each hydrant (painting, inspection, flushing, etc). This new functionality is excellent and I look forward to seeing Collector evolve over time. I do currently have one complaint/suggestion:
It would be nice to be able to allow our operators all the options that they need to create and save new management records in our related table using Collector, without being given the option on the main screen to create new features. In this case, there is no need for an operator to add a hydrant to the database because every hydrant that is in the ground is already in the feature table. Its not a huge problem, but my guys do have a self-proclaimed tendency to fat-finger buttons and work their way into the furthest corners of our mobile apps by accident. It would make a big difference if the first screen in Collector didn't offer my operators the chance to "Collect New" a hydrant, but rather only showed the feature layer legend (or if it just popped up it's first menu based on a user selection of a feature in the feature layer).
Right now when sharing a shapefile as a Service to AGOL - under Feature Access - we are allowed to Create, Delete, Querey, Sync, and Update. When publishing a relationship we must select all 5 in order to allow for the functionality we need to meet Collector's relationship class requirements, and to see that pivotal "Add New" button at the bottom of the primary pop-up. Ultimately my suggestion would be to create the ability to separate the functionality of related tables and features (or feature to feature, table to table, etc) so that you could check on 10 boxes to achieve the same results currently supported - OR - only choose to query, sync, and update the feature layer attributes (hydrants) while choosing to access all 5 operations to update the related table (management records).
