I love it. 
If the shape extends off screen due to zoom level, selecting it doesn't adjust zoom to extents of selected shape. It does appear to centre the first (?) vertice on screen? Could it trigger a similar action to the existing zoom-extent map button but for the selected element?
Selecting a shape is only possible by tapping a vertice, not on an edge or interior, this is ok but my first reaction was to tap inside the shape, I'd add user guidance for this as a hint in my forms.
Close / overlapping shapes are discernable as there's no shading, and selection is easy enough by tapping a vertice even if it's "inside" another shape. (Very similar shapes would have similar issues selecting them to very close points as previously mentioned)
With Google-streets basemap with/without a tileset, when the shape overlapped with a building element, the edges/lines were greyed out as if the building was partially transparent and above them, but below the vertices. Seems to only affect this particular basemap.
With raster tilesets in other basemaps, the lines appear over the top of the tileset as in geoshape widget
Mixed formats - All three can be represented at once, doesn't matter what's in the geometry column. I hadn't expected this, but it's great.
Error handling - I opened my updated form (CSV had geometry values as polygons not points) in an older non beta version, and they displayed as points. I didn't check which point (first/centroid etc), but this was a graceful fallback.
There is no apparent visual change in selected shape - remains as red lines with white filled red circles. A change in colour, line weight, vertice style/fill or perhaps colour and modify line style from solid to dashed for colourblind people would help.
The top shape is selected here:
Running on an old Galaxy S5, so it might not be representative: Mapbox basemap is horribly slow and result in ODK Collect isn't responding notices. Google basemap is much snappier on the same device. 31 rectangles in the test select. I haven't compared this to select a point on this device.
Testing the same form on a Galaxy Tab S7 there was no noticeable slowdown, so not a real issue for me, but it did just crash when switching from google to mapbox and opening the select from map question, hasn't repeated yet. Edit happened again when loading select from map, without switching basemap first.
