Degassing - if it's like my Marauder, they sell a "Degassing Tool" that screws into the back, and allows depressurizing of the chamber. Otherwise, just shoot it until it's empty. No damage like springers, it's just a valve letting air out.
The Discovery in .22 shows 900 FPS with lead pellets. Approximately 25 FPE.
The Maximus shows 850 FPS with 23 foot pounds at the muzzle. It's 2 FPE difference. Not sure that's a deal-breaker for me.
The hardwood stock on the Disco increases cost, and weight. If hunting, I like the synthetic better as I'm not afraid to scratch it up, but to each his own.
To show how closely related the guns are, they share the same owners manual
I suspect the difference is specs is just due to variations in testing, or possibly test pellet weight.
And, yes, the owners manual shows the de-gassing tools in use for both guns.
If I had to guess, I'd say the Maximus is just a cheaper version of the Discovery, mostly in synthetic stock instead of wood, and not a whole lot else.
I still stand by:
Used Marauder - Gen 2 only, and only if I get a chance to send a hundred or so pellets downrange
Discovery with pump - no, I'd get the Maximus with pump instead. Fundementally the same gun, lower price.
850 - for a first gun, no, don't care who put it together, need a community to fall back on, and Marauder and Maximus both have communities.
Disco and Maximus have reputations for low maintenance, which is something important for a newbie, so considering how complete the Maximus kit is, and value for price, that's still where I'd go.
If I hadn't just purchased a 1701P, I'd probably be buying the Maximus Eruo version. At $165 I could set it up as an entry level field target gun.
As always, just my opinion. Had the Maximus been available before I bought the Marauder, I'd probably be a proud Maximus owner instead of a Marauder owner.