You can't withdraw bonus bets or bet credits, but you can withdraw winnings. Bet credits and bonus bets cannot be withdrawn, but they can be used to wager on other sporting markets your sportsbook has to offer. Some sportsbooks make you use your bonus funds or bet credits in one lump sum.
For each matched bet, you can typically expect to extract 50-80% of the free bet amount as profit. This is because betting exchanges usually charge a commission on winnings. You may also make a small loss on the qualifying bet due to the minor difference in odds on each website.