I have both products. I like Last Preservative and do not like Groove Glide.
Last reduces noise with little or no change in overall tonal balance, dynamics and bandwidth. More importantly it drastically reduces record wear for dozens of plays.
If an attribute had to be assigned to magnify the sonic differences between Last and Groove Glide, Last is VERY slightly brighter sounding (you must really listen to pick up on this) while Groove Glide lessens immediacy and impact of all frequencies, but particularly the high frequencies.
It's likely people will disagree on which is better depending on their cartridge and overall system balance. A friend that owns a "hot" Clear Audio cartridge prefers Groove Glide but when we listened to an LP treated identically but using my Koetsu Rosewood Signature Platinum, The Last was clearly superior.
I might add here, I never treat with Last and then immediately play the LP. I always do an additional rinse using Record Research and my VPI record cleaning machine.
Once Last has done it's job (the first few seconds after applying), it has done all it will do. However, I believe it leaves behind some audible impurities as the RR fluid is a must on my system. With this final rinse, I wind up with all the advantages of Last and no disadvantage that I can detect.
You may also do a final wash with RR fluid after applying Groove Glide, but the Record Research will remove it completely, putting you back to an original untreated LP.
I have LP's that were treated with Last in the 1970's and still play as new. Even if the performance of these two products was identical after treatment and first audition, I would still choose Last because It has proven itself over time.
