Prepayment penalties- usually 1-5 year terms.

A Heloc is a open end mortgage like a credit card so its an additional trade line on credit, cannto never be used as an Asset, PITI reserve, and its a DTI killer in most cases.A heloc is also usually set up on a shorter term versus a mortgage, carries a Higher interest rate, and most carry a interest only with a prepayment penalty.

Yes you are giving up a rate that you probably aren't going to see again anytime soon, but as long as you aren't locked into an extensive penalty period you can always refi again if rates plummet to the point that it makes sense to do so. 

One of the investors we are working with has a score around 680 but is looking at high 6's with a one year prepayment penalty. 

They even provided penalty relief because he contacted them first.

These seasoning periods are usually anywhere from 3-12 months and there are prepayment penalties that range from 0 (buying the prepayment penalty out to 5 years or more).

New Mexico has an unfortunate law against prepayment penalties for DSCR Loans on 2-4 unit multi that requires higher rates, but they don't apply to 5+ and I've seen some people have success with that size range in NM

Good news is that he historically has paid on time and when late, paid the prior months + the penalty.

However, the substantial price increases and lack of inventory have lead me to start buying tax deeds, which Georgia is a penalty state offering a 20% (non-prorated) premium. 

If you get it wrong, the penalties will get costly quickly.All the best!