F2P won't work long-term, just as any promotion or sale hasn't in the past. I'll explain why.
Both those methods will work at getting a spike in activity short term, which is great. However, after the "honeymoon phase" with the game wears off, people will leave. They will leave because this game isn't supported with new content that people want (guns, ships, maps).
From my calculations, MUSE has created 7 new ships, 7 new guns, and 7 new maps since the release of skirmish (factoring in both skirmish and alliance content). That is 1.75, or 2 (rounding up) new ships, 2 new guns, and 2 new maps a year that they have produced.
Unfortunately, that is my minimum expectation of content that should be produced and available for skirmish at this point. This is even factoring in Alliance content, which should double that. Basically, MUSE is 4 years behind in expected content, and this is a problem that others, and myself, have tried communicating to them for these past 4 years.
That is a huge problem with the game, and a reason why not only veteran players, but entire clans, and casual players from sales are not returning, and why advertising will have diminishing returns (to the point of being completely ineffective).
This game will continue to bleed players, F2P or not, until it begins to provide new (meaningful) content on a consistent basis.
Basically, they've wasted 4 good years of opportunity to add to their game and keep their community strong, and I don't see how they can bounce back from that.