You can use these exercises if you can do them with a significant addition of weight for VERY strict reps AND can do at least 12 reps without any added weight in strict form, otherwise you wont be able to do the 6-8 drop.
For example, after 4-6 cluster reps you would likely be able to use about 65-70% of your max for the 6-8 reps part.
If you are 200lbs it means that this 200lbs has to represent 65-70% of the weight you can do on chins or dips to be able to do this technique.
In other words a 200lbs needs to be able to do a strict repetition with 60-70lbs added resistance on either chins or dips if he wants to use those exercise. The minimum strength level you need to have to be able to use this method with chins or dips is adding 30% of your bodyweight for one super strict rep.
Our 200lbs individual who can do one chin-up with an additional 70lbs (total weight of 270lbs) would then use:
Cluster part: 270lbs x 85-90% = 230-245lbs... since his bodyweight is 200 this means adding 30-45lbs
Drop set part: bodyweight only
If someone isn't able to do chins or dips with at least 30% more than his bodyweight he shouldn't use these exercises and personally I would prefer if he can do 40%,at 30% the last 2 sets will likely be too hard.