Let's compare! All boost and +1 for 1 resource. All are Assets that need to be played, generally costing 1 action.

Physical Training 2 resources to play, icons
Physical Training (2) 2 XP, 0 resources to play, icons
This card is 4 XP, costs 2 resources to play, icons, and gets 2 recurring resources for boosting.

Pros

• They all boost things most Guardians want boosted; while they tend to have 4-5 , there are a lot of enemies with difficulties that high, so pumping is nice. Similarly, Guardians tend to have 3-4 and there are a lot of 4-5 Treacheries.
• For the level 2 and 4 versions,resources are turned into bonuses immediately.
• Recurring resources are great; there will rarely be a turn where playing them won't help, and they can preserve using cards for icons, since Guardian tends to have sort of weak card draw.
• Levels 2 and 4 combo well with Well Prepared.
• They are slotless Assets, something that slot-starved Guardians will appreciate.
• Lots of Assets protect Guardians from Treacheries like Crypt Chill and Corrosion. That's not a happy use, but better to lose your booster rather than your weapon while you are engaged....

Cons

• They aren't permanent.
• They don't help with Guardians' really weak and .
• They are expensive to run, and Guardians have weak economies, although the Nathaniel Cho deck has offered some alternatives, and Big Money Leo is a thing.
• They are expensive, and Guardians already have a lot of other Assets to spend XP and resources on.

In general, if you want to "pay to pass," all of these are decent cards and give a clear progression to build up to the Level-4 version, which is definitely the best of the lot, assuming you have the XP to spare.

TL;DR AH:TCG is a land of contrasts, and some deck styles and play preferences will like these and others won't.

I’m surprised nobody has mentioned the usefulness when paired with Heroic Rescue. You can take the attack that would be directed against another investigator, do an auto damage, and get an attack. Nice simple 3 damage, and a feasible way of killing a pesky 3 health enemy engaged with another investigator (Which forgotten age has plenty of!) though with a risk of collaterol damage to your buddy!

Tamest basic weakness in the game? It doesn’t cost you any actions at all to deal with, all it really does is cost you a card and maybe a test or two down the line. Draw it late? No issues. Playing on expert? You have testless options abound anyway. Playing with new cards that care on any level about curse tokens? This is actually beneficial to you. And finally you might actually be using cards that convert curse to bless, in which case this is easily circumvented. This might hurt more in Innsmouth depending on what the scenarios do with curse and bless, but outside of that campaign, this seems incredibly easy to deal with.

EDIT: I take it back, only because Day of Reckoning got spoiled unexpectedly. Check that one out for an even tamer weakness.

Combine it with Dayana Esperence and low cost powerfull spell like Deny Existence. Shining Trapezohedron will cancel the additional cost (spend secret and exhaust Dayana) and allows you to play Deny Existence each round after passing 0 test.

Note that this search only checks the encounter deck, not the discard pile (and victory display). For that reason, it's a good idea to advance "Harlan's Curse" when all 3 Acolytes are in the discard/play (or even just 2 Acolytes in the discard/play when 3/4 player) - this prevents the spawn.

Of course you might be dealing with the other version of this act, so this gambit might have no effect. But if it works well, it can be nice.