I have and run both.
You can read a full review of the newer HSS kit
here.
The Galaga Enhanment Pack is great and solves the following:
High score save keeps scores after the board has been powered off
Support for 8 digit scores! Players can achieve and record scores up to 99,999,990!
Fast or original fire speed - selectable per game, per player. Choose speed from on screen menu!
Fast power on test. Most of the on screen testing is bypassed, start up is 80% faster!
Level 255 lockup fix. For those who can reach level 255... The game is not over.
Adds support for FREE PLAY on Gallag and Nebulous Bee bootleg PCBS! No need for
opening the coin door or adding a credit button! (Note: Freeplay is optional by setting the dip switches 1, 2 & 3 on)
Support for Gallag and Nebulous Bee bootleg PCBs!
Title change from: "GALLAG" or "Nebulous Bee" on the attract screen to "GALAGA".
The newer kit that HSS offers just takes what Mike started to another lever with more options and on-line scoring. There are also several cool "Easter eggs" that Joe put into the game as well. The basic game play is not changed at all.The best part is the ability to switch game modes just by pressing the player one start button for 4 secs. Not need to dive into the settings menu at all. You have more control over the attract screen as well which is cool.
The HSS kit gives you more options:
Fast boot - No waiting for initialization.
Attract Mode with Free Play and Attract Sounds!
8 different high score tables (for each setting in the game menu!)
Different settings need different HSS tables, right? ie. Auto Fire at Hard Settings, Normal fire at Easy, etc.
On Screen Game Menu (Fast selection of each game mode)
Extended scoring (up to 99.999.990 points)
Real Attract Sounds NOT JUST A FEW BLOOPS and BLEEPS! (switchable from off, 25%, 50%, or 100% of the time)
Attract Mode with Free Play and Attract Sounds!
4 different shooting speeds - Normal, Slow, Fast, Fastest
Auto fire option - Turn it on or off with a quick on screen change!
Level 255 fix. Now you can go up to 65000+ levels! Difficulty does not go higher than 255 (only the counting goes higher)
Saves scores without using failing NVRAM
Easy dip settings via on screen menu
Optional ROM Saver
Can't go wrong with either one honestly.