Presuming that the 260 and 1490 work the same way as my 1390 you should have no problem using a single directory structure for two devices. From my experience so far the POI loader does not write to or modify your source POI files, it reads them, builds the POI file and writes it to the appropriate place on the device. You should be able to connect your devices to your PC update the first device from your source directory using the POI loader and then do it all again for your second GPS.
Works with Nuvi 260 AND Nuvi 1490T?
