What is your data transfer speed via USB?

Seems normal, I don't expect that Garmin uses fast flash memory, there is no real reason for it. And updating the maps in a while acceptable at this speed.

I agree that for common usage watch do not need a fast storage. But updating big maps or coping music (to or from watch) can made a pain if you a hurry. Who knows, maybe even objects on map during activity or on zoom/move will updated faster. However I don't want to discuss reasons, I want just compare what speed have another users.

Keep in mind the file system on the 945 is MTP, so not a mass storage access.

MTP is different:

Performance[edit]

• (-) MTP allows no parallelism, unlike USB mass storage or NAS. MTP has been built to only allow a single operation simultaneously (for example: read, write or delete operation), while no other operation can be executed until the previous operation is complete.
• (-) Limited support for transferring parts of files, such as blocks or byte ranges (see § Direct modification and partial transfer features).
• (-) Limited support for direct modification of files (see § Direct modification and partial transfer features). To modify a file or its metadata, the whole file may need to be copied out of the device and reuploaded, which takes a long time for a large file or directory, and blocks the device for other operations in the meantime. Google's MTP implementation in Android includes extensions to deal with this limitation; however, these extensions must be supported by the host operating system.^[7][8]
• (-) Loading longer file lists (thousands of items) and "preparing" for transferring files might take longer than the file transfer itself.

Transparency to MTP-unaware software[edit]

(-) Windows does not assign drive letters or UNC paths to MTP devices because it does not natively expose them as virtual file systems. Without drive letters or UNC paths, MTP-unaware software cannot access directories or files on these devices. The user has to switch to an MTP-aware application, or else work around by using an MTP-aware application such as Windows Explorer to copy or move the file to a file system that the application can access.

One specific concern is that antivirus software on the host computer may not be aware of MTP devices, making them potentially less secure than mass storage devices (although if files on MTP devices are copied or moved to the host before use, MTP-unaware antivirus software will have a chance to scan them).^{[citation needed]} Antivirus scanning might also be impractical due to blocking regular use of the device.

https://en.wikipedia.org/wiki/Media_Transfer_Protocol

Thanks to all for answers. The question is closed for me.

(this is very pedantic, and certainly not relevant) MTP is just the transport protocol, not the filesystem. The filesystem is very likely just FAT32.