If you try to open a locally stored file in any of the Google Apps apps, you'll see that the filename is truncated after about 10 characters -- often meaning you can't tell one file for another (especially for revisions). Google Drive shows a wide filename, but not Docs, Sheets, or Slides.
Wait till you try to save your changes! There's no save option for PowerPoint-formatted files, and when you exit the file, your changes are discarded -- not saved automatically as you'd expect. The More menu's Share & Export submenu has the option to save the file to the native Google Slides format. Get used to it if you want to your changes to take -- then losing Office compatibility until you export it to a native Office format later. (The desktop Web version works the same unintuitive way, incidentally.)
Docs and Sheets do save your changes when you close your Microsoft Office files, no conversion required. What seems to be going on with Slides in iOS is that takes a long time to sync the changes back to Google Drive, so it loses the changes. In my tests, I ended up with multiple copies of the same document, likely from each time I opened it and redid my changes -- almost always without the changes I had made. When I used Slides in Android, the changes were saved, even if I ddn't convert the files from PowerPoint format to the Slides format. This is clearly a bug in the iOS version of Slides.
If you remember those early-20th-century Keystone Cops films about comedically hapless cops, you get a sense of what it's like to deal with files in Google Apps in iOS.
A slideshow tool that can do only the basics
When you open a presentation in Slides, you quickly discover you can do only the basics with it: Edit text, apply text formatting, move and delete items, add photos and shapes, view and edit presenter notes, and move, delete, and add slides. In other words, you can touch up presentations and create basic ones -- that's it. You can't control slide transitions, apply animations, spell-check, or execute any of a dozen more sophisticated tasks you can do in Apple's Keynote for iOS, Microsoft's PowerPoint for iPad -- or in Google Slide in a desktop browser. And note that resize handles respond to your gestures only intermittently, so resizing elements is a hit-or-miss proposition.
If you are a salesperson or a conference presenter working on your iPad on the road, you won't want to use Slides. If you're a Google Apps shop, your staff will need to bring your laptop -- or go rogue and use Apple's Keynote. (You could use Microsoft's PowerPoint, but its iPad office suite requires an Office 365 subscription, and it's not as adept as Google Apps or Apple iWork at working on files across cloud storage services.)
Sign up for CIO Asia eNewsletters.