Sounds like you are a reloading newbie?
If so, forget seating gages, you really don't need that extra complexity yet and it would be of little help. Just go by your loading manual's suggestions for seating depth instead. And understand that the book OAL is NOT a "law", it's just a suggested starting place, same as the powder charge data.
Ditto bullet comparitors, you are unlikely to need one now. Later, when you are totally comfortable with the basics is plenty soon enough to get one of those. You will know when you are ready for that, all by yourself! Sure, BR shooters have reason to measure off the bullets ogive but sporter rifles and bullets rarely, if ever, will notice any difference when measured off the bullet nose!
You WILL need a way to measure case lengths and loaded OAL. That's best done with a 6" stainless steel dial caliper that reads in thousanths of an inch. Those sold by Harbor Freight Tools and MidwayUSA (do a web search if you aren't familiar with them) are plenty good enough, as good as any other sold for less than $100 anyway.
Don't be confused by the widely varying prices from various reloading brands, they are identical to the less expensive ones which are frequently on sale at HF for as little as $12, all are actually made in the same Chinese plant. Spending more here will get you nothing. Do get a dial type, the attractive digitals need new batteries too often and are no more accurate.
