I've yet to use the STEEM version of Freewallet, but I can offer that for whatever reason their wallets operate a lot better on the Android OS than they do Apple's.
Regardless I'd recommend sticking with the wallet provided on Steemit. There's no sense in transferring your STEEM to Freewallet only to be charged a fee when you want to send it over to Steemit.
However, if you wish to trade another crypto for STEEM, Freewallet is a good option in that regard because I don't believe a fee is charged to do so like Shapeshift.io & Changelly just make sure that you send atleast the minimum balance otherwise you're SOL. If you wish to use BTC to purchase STEEM you can do so right in the Steemit wallet at the best market price with no fee. I believe this to be the best coarse of action when it comes to STEEM.
I know I wasn't able to provide the answer you were looking for, but I hope I was able to offer some benefit in regard to your query.
Regards. V