[Milestone XT720 Android Development] kousik:
I had exactly the same question. I have firmware built for India and doesn't match any of the recommended one in droidforums. And I didn't want to disturb my stock one either, unless necessary. Then I opened up one of the optimizer script and looked inside. And the bad news is, if the optimizer script does not match your ROM, there is a high chance that things will go wrong. So I checked what would that be, and I edited "install.sh" as per the configuration of my ROM. The first difference, which will completely mess up your phone if there is a mismatch is mount device of /system. In other ROMs it is /dev/block/mtdblock6 but in the device I have it is /dev/block/mtdblock7. So this was a must change in my install.sh:

--- install.sh 2010-10-15 13:48:04.000000000 +0530
+++ \Temp\install.sh 2011-01-04 16:09:36.000000000 +0530
@@ -31,7 +31,7 @@
echo $message
echo ""
#remount the system partition as read/write
- mount -t yaffs2 -o rw,remount /dev/block/mtdblock6 /system
+ mount -t yaffs2 -o rw,remount /dev/block/mtdblock7 /system

echo "Which option would you like to install? (1-9)"
read x

Because unless /system is remounted correctly rest of the script won't work at all. And then "build.prop", if you just copy the script's build.prop it'll overwrite many things of your build. Instead, patch your build.prop with the following:

--- build.prop.original 2010-10-08 08:27:36.000000000 +0530
+++ build.prop 2010-10-15 13:47:26.000000000 +0530
@@ -49,15 +49,16 @@
# Time between scans in seconds. Keep it high to minimize battery drain.
# This only affects the case in which there are remembered access points,
# but none are in range.
-# ST_SKT changes from 15 to 45 to lessen battery drain loss for a reference from HTC phone
-wifi.supplicant_scan_interval = 45
+# ST_SKT changes from 45 to 90 to lessen battery drain loss
+wifi.supplicant_scan_interval = 90

# The OpenGL ES API level that is natively supported by this device.
# This is a 16.16 fixed point number
ro.opengles.version = 131072

# This is a high density device with more memory, so larger vm heaps for it.
-dalvik.vm.heapsize=28m
+# LauncherPro, ADW Launcher, and some games have problem if this value it set below 32m
+dalvik.vm.heapsize=32m

#
# ADDITIONAL_BUILD_PROPERTIES
@@ -71,7 +72,8 @@
ro.config.notification_sound=Grass_Meadow.ogg
ro.config.alarm_alert=Alarm_Classic.ogg
ro.telephony.call_ring.multiple=false
-ro.telephony.call_ring.delay=3000
+# Lower delay between notification of call to handset and when ringer starts
+ro.telephony.call_ring.delay=800
ro.url.safetylegal=http://www.motorola.com/staticfiles/Support/legal/?model=Mil
estoneXT720
ro.setupwizard.enable_bypass=1
ro.media.enc.hprof.file.format=mp4
@@ -80,7 +82,8 @@
ro.media.enc.hprof.vid.width=720
ro.media.enc.hprof.vid.height=480
ro.media.enc.hprof.vid.fps=25
-ro.media.enc.hprof.vid.bps=3000000
+# Increased bitrate to 6Mb to increase 480p recording quality
+ro.media.enc.hprof.vid.bps=6000000
ro.media.enc.hprof.aud.bps=96000
ro.media.enc.hprof.aud.hz=16000
ro.media.enc.hprof.aud.ch=1
@@ -137,3 +140,15 @@
ro.com.google.gmsversion=2.1_r7
ro.setupwizard.mode=OPTIONAL
ro.com.google.locationfeatures=1
+
+# This line is supposed to keep the backlight for the buttons on when the screen is on
+ro.mot.buttonlight.timeout=0
+
+# This line is supposed to optimized the proximity sensor to turn screen on faster during call
+mot.proximity.delay=150
+
+# This line is supposed to help with redraw lag
+windowsmgr.max_events_per_sec=60
+
+# This line enables JIT
+dalvik.vm.execution-mode=int:jit

So the bottom-line is, you do not need to flash any of those firmware, you can still apply the optimizer script, provided the script's assumptions matches your ROM. In case it doesn't (like mine), edit install.sh, build.prop suitably before running the script.