TL;DR: Should You Pull?
Sync Pair Analysis
Glacia & Glalie is an Ice Support Sync Pair of Pokémon Masters. This couple comes with various Co-op benefits to your team when it comes to recovering from assaults. What is really unique about this Sync Pair is that Glacia is the very first Sync Trainer who has a Mega-Evolution of a Sync Pair that isn't designed to battle but Support.
Can Tank Anytime
Glacia's "Attention Here!" Support move will allow Glalie to taunt all opponents. Enforcing them to focus Glalie, stepping ahead of your fragile damage dealing allies Sync Partners, a move that can have uses in Co-op play. As a side note do note that Glalie can tank another time by Sync Moving
Glacia is a teamplayer with her second support move "X Regen All" Makes all Sync Pair Allies gradually heal themselves.
May Freeze The Enemy
To begin with, we have to note that it is merely a small chance but, Glalie comes with two offensive moves, one being an AoE "Powder Snow" allowing Glalie to target all opponents, while the damage output is rather low, it only costs one gauge, and it is something one should use while tanking and healing allies, where there is hope for freezing the enemy.
Overall Horrible Base Stats
When you look at a Sync Pair in Pokémon Masters, so far it has always been clear on where their strengths lied at, but when looking at Glacia & Glalie it is just low on all departments that they are considerable one of the worst Sync Pairs in comparison to other Support Sync Pairs Stats-Wise.
Doesn't Really Do Much Outside Of Tanking
Glalie might take all aggro from the enemies, and then might heal your allies, but what is the plan after that. The damage capabilities are very low.
In Co-Op Glacia & Glalie should be paired with Striker Sync Pairs, where Glalie can keep the aggro on themselves while allowing their allies to safely do as much damage as possible without having to be feared of being targetted, even if they take AoE hits from the enemy Glacia & Glalie can help them heal themselves.
Glacia & Glalie is a baby version of the following two Sync Pairs. Cheren & Stoutland, Acerola & Palossand. As they are both unlocked through story it is recommended to try them, and see how the taunt and graduat self-heal works, if it is to your liking then you will perfectly understand Glalie's Co-Op capabilities.
I've yet to use a Sync Move on a Support Sync Pair outside of Rosa & Serperior's Sync Pair Stories with Evolution. So I hardly see when it would be possible for anyone to achieve Mega-Glalie, but it is a possibility as Sync Move is another form of AoE Taunting the Enemy Sync Pairs.
Overall The Sync Pair lacks in stats, and their status conditions are low chance. Therefore sadly it is a No.
If you are curious about the AoE heal, or even the taunting you should try out the Story Characters who has similarly moves and see for yourselves if this is something you can use.
At the current state of the game, Glacia & Glalie aren't needed. If you do manage to pull the Sync Pair don't be afraid to use them, as they can tank a lot.