No problem straight up, it doesn't contain much but enough nutrients and it's not hot at all. That's what I use to start seedlings, or the odd time I plant clones straight into soil (use aero cloners for the most part, unless I don't have the room to run the cloner).
For seedlings, no different than clones if I do them in soil, I use a party cup and leave it in there until about 2-3 weeks and let them establish well and build a decent root system before transplanting them into their final or larger pot. I put a mix for about 2/3 of the cup of 50% Pro-Mix, 50% Triple or Quad mix soil (hot). Then for the final (top) 1/3 of the cup, where the seedlings will sit initially, I use straight-up PRO-Mix. That way by the time the roots establish and reach the "warm" soil, they can handle it. I did this over time with a lot of trial and error, works well for me and avoids burning them.