If an angel want to put in money (say 300k) but is really an AngelList syndicate, is there anything to be concerned about?

Unless the angel has a very large following on Angellist we find that angellist syndicates are better for closing rounds with strong leads vs getting an angel check. You won’t know for at least 3 weeks if in fact the 300k will come in and you have to invest time in promoting your profile to make it look good. If the 300k is guaranteed there is no issue with the entity that is investing that is materially different from any other investor. The big difference is you still need to sell the syndicate on your company and you will be exposing it a lot more publicly and need to be ok with that.