Here's a somewhat generic answer as it relates to the Value Series, of which the M915 is part of.

The Value Series guns saved on cost by:

1- using plastic parts, to include some sights, as opposed to the standard production guns using Novak sights.

2- single side safeties, instead of ambi safeties as found on the standard production guns.

3- Frames had less milling, resulting in the Value Series having more of a straight frame profile, with no "step" in the area just above the dust cover. Interestingly, you need to be careful with holster selection, as with closely formed holsters made for some standard production guns won't work with their Value Series counterparts due to the frame differences.

4- back to plastic parts, some of the Value Series guns had plastic guide rods, while the standard production guns had steel.

Not all the above are negatives, but they saved production costs - allowing the Value series guns to sell for less.

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.............SmithNut