I have been doing a lot of simple ETL using FME Desktop, but ran into some problems with writing directly to ArcSDE. So I ended up just writing back to SHP and exporting to SDE from ArcCatalog.
Turns out I was using the wrong writer. Insetad of using the ESRI ArcSDE writer, which writes directly to (in my case) SQL Server but doesn’t utilize ArcObjects, you need to use the ESRI Geodatabase (ArsSDE) writer. Other wise you’re creating tables in your database but they’re not registered with the geodatabase. I figured this out the hard way when my newly created feature classes didn’t show up in ArcCatalog but I could see them in SQL Server Management Studio.
What I like about FME is the simplicity. I’ve read that FME speed outperforms Python scripting. I suppose that’s true. I haven’t run any tests. But when it comes to ESRI geoprocessing, I much prefer FME over the ESRI tools even for simple tasks. Using the a few wildcard characters and merging feature types is a lot easier than having to worry about matching schemas, gp.workspaces, or glob.glob() searches with ESRI Python.