Yes, this is correct!

With Braiins pool's share scheme -- Pay Per Last N Shares (PPLNS) -- you're not guaranteed a payout like with (Full) Pay Per Share (F/PPS) pools, which do pay the hashprice in sats/TH/s/day worth of work contributed.

Also, Braiins has a 0.001 btc or 100k sats payout threshold (all pools i'm aware of have payout thresholds)

Braiins however uses a fixed payout fee for under 0.01 btc or 1M sats (which is unique to them and not great imo).

With Rigly's "test drive" you're bascially paying 500 sats to try out mining. It's not necessarily going to pay dividends, but still, for a quarter you get real hashrate and could also potentially make a buck's worth of sats if you're lucky and Braiins finds a block, so there's that. Notice however, with 3 hours of hashrate you are v. unlikely to meet Braiins payout threshold.