I think "good" when talking about your ROI % is something you need to decide for yourself.I know that with MUCH less risk, less thinking, less work and effort then REI, I can make 8% safely with my money.So for me, I would have to be in low double digits plus to entice me into taking a risk with REI.  

The Mobile homes themselves will either be treated as 27.5 year depreciation or 5-year 'personal property' if the homes still have the wheels and axels on.As far as the cost and benefit, most firms will give you an upfront quote (but self promotion is not permitted here 😉)One cannot answer whether or not this strategy is worthwhile for you, since we don't know your tax situation, and how much income the park is producing, or if you can use that depreciation to offset other income.

Its these kind of survey's that the investors or promoters hang there hat on and its not reality in the real world Kind of like Zillow is for values  :)

I'm entertaining this option myself for my upcoming duplex house hack (if a value-add deal is enticing enough).Also, thanks to @Roy N. for the great book recommendation.

While there are several companies that provide these services and do it the right way it is often promoted as a way to get rich quick with little money on someone else's dime. 

If the goal is financial independence you'll get a far greater ROI (at least in the beginning of your journey) by putting in an extra couple hours a week at your job to get a promotion than spending that same amount of time, plus whatever capital it takes, to get a property that will cash flow ~$100 a week for example.

Instead, you could read books, listen to podcasts, and follow the right people on social media that add more value than promote their course.

The rate I was quoted was 7.125% with 2 and a half points purchased ( I have good credit at 750+).Moreover, there is a promotion from the turnkey service where the first year property management fee is waived, therefore it is not listed as an expense on the proforma, which only covers the first year.

When I got the card, they had a promotion that it was 3% interest for the first 6 months, now I'm at 7%.

It is free unless you want to promote your listing for more views.