It’s not about whether or not he honors them. The effectiveness of those preemptive pardons can be adjudicated by the SC. But there’s a couple of considerations on that front:

• will the SC concur that blanket pardons in advance of any charges are actually allowed?
• will Trump want to challenge that, since it would potentially kneecap any effort he makes later in that regard?

But also:

• will Trump or the SC give a shit about the blatant hypocrisy and double standard if they do strike down this sort of thing from Biden, but let Trump do it? (IMO probably not)
• if the SC gives a shit but Trump doesn’t, what’s to stop him using leverage and/or stochastic terrorism to help accelerate the conclusion of one or more justices’ tenure so he can slip someone more agreeable in?
• will the judicial branch even exist in an independent fashion in 4 years?

TL;DR: who fuckin knows at this point