I don't recommend metaexchange until they fix their rate reporting. the rates listed on the site are admittedly bogus and not what you can expect to receive. It apparently only affects a couple markets though and is a temporary 'experiment', so BTC:bUSD may be fine.
The BTC->bitUSD pair does not use the liquidity based pricing. The pricing is completely based off the internal market; a spread against what BTS:bitUSD is actually trading at. It's probably why I'm buying BTC for 199 bitUSD vs Blocktrade's 160 and selling BTC for 212 bitUSD vs their 231. Shapeshift is paying more for BTC (212 vs 199) but are charging a lot more for it (251 vs 211).
There is a good reason they may be working with a 44% spread. There is a fairly large price disparity between the internal and external prices of BTC. I think I can make a go of it with my relatively narrow 6.5% spread since I'm seeing a lot of volume in and out. As long as I can avoid having to refresh funds on the external market it should work out.
However you raised another point that i think needs addressing: Locking in the price. The timing of this should be when the currency is first seen on the network. For Bitcoin and Bitshares this is close enough to instant. The long transaction times of BTC mean holding the price open until it settles can result in not getting what you expect. Sometimes you'll get more and sometimes you'll get less. Guess which is the only result we have ever had reported . Anyway, I recognize that as something that needs to be fixed.
I shouldn't have said metaExchange as a whole, as I've had no issue with most of their markets. Just the BTS:BTC market.
I would be ecstatic if metaExchange, or whoever, offered instant lock in. That would really take the guess work / risk out of moving liquidity around from market to market(for me anyway), but I understand the need for confirmation. That risk is not my complaint. I can deal with the risk that the market moves against me within the terms of a trade. The only issue I had with mX is the rate on some markets are not as advertised. If you can only get the 1BTC= XBTS rate when you trade less than .01 BTC
, and not when you trade 1 BTC then the advertised rate is misleading. Perhaps something more like blocktrades rate discovery would be beneficial. So long as I can find the rate I can expect, there need not be any issues.
The BTC:BTS market is the only one I had this experience with. I've not had any issues (that I noticed) with BTC:bitUSD. : )