Best way i've found to use them is for captcha-less rolls. But now seems to be harder and harder to keep a good amount of RP on hand, as they burn out so quicly.
Instead of spending your RP for captcha free claim, you should just unlock the free bonuses to play without captcha on your account. It is different between accounts and it might not stay forever but compare with using RP on the free claim.
To max out your RP, just go for RP bonus instead. Provided if you could claim for more than 12 times a day , otherwise dont because you need 12 times just to get back the RP that you paid for the bonus
I wrote this exactly 1 month ago on this thread lol. It seems people pay no attention to this lol
There are actually some requirement to play without any captcha as well unlocking all the RP redeem bonuses
This is what it looks like in a (almost) fresh account
This is different depending on your account and you can check it by clicking the requirement to unlock bonuses on the landing page. Also according to this fresh account, 0.00530847 BTC is around $50 as of now. The cheapest option would be to purchase lottery ticket which cost 2559 satoshi or either wager 10k satoshi , whichever works best for your account