With training (where you'll also learn how to do a proper Briefing before ever getting near the airplanes, amongst other things): Safe enough.
Without training: Today is a good day to die.
I'm not kidding. It is not as easy as it looks.
You'll be surprised at your first turn as #2 just how much you'll have to be constantly doing to hold position.
As lead, you MUST be 100% responsible for the safety of your wingmen. They are staring at your strut and busy as hell. Especially when they're new to it.
Examples:
Turning into the new guy when he's badly sucked and just firewalled his throttle to get unsucked is not nice if done rapidly, since you just shortened the distance to you considerably. But is nice if you're gentle and trying to help him close a large gap. IF you know he's expecting it.
You can't just fly up front fat dumb and happy and not think about what the other aircraft have to do to stay with you. Judicious small smooth adjustments to throttle can help your wingmen too but new folks would probably prefer you just fly a nice consistent speed and altitude so they can figure out how the hell to stay in one place in reference to you.
You get to know what your group will do over time.
Radio procedures are different at first also. Lead talks. Everybody else acknowledges quickly. Then shut up.
Grab some folks who know how to do it right and give it a shot. It's fun as hell and if I had the opportunity, I'd do more of it with people I trusted. It's also a lot of work at first. Most training will start loose and then tighten it up as skill levels are exposed and honed. I don't have nearly enough time doing it to be commenting, or competent.
I could muddle my way through being a safe #2 starting loose and closing it up a bit. That's about as comfortable as I'd go without a few hours with a good (or at least briefed and predictable) lead. A new lead? Forgettaboutit. I'll stay loose. Dork-boy over there might decide he wants to bank hard into me without warning. "Targets merging" is a non-fun way to end a fun flight.
It'll make your appreciation go WAY up for the airshow teams too. They bust their butts to make it look easy and good in all sorts of conditions while lead is maintaining safety from the centerline and making all the magic happen at show center and staying in the box. Much more impressive once you've had a little taste of it.