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The user manual for the ES unit mentions a 13.5mm distance. It is not very apparent but I believe this is the extra inward travel you will need on your focuser. The Tele Vue Paracorr 2 has a similar distance of 14mm.
A coma corrector can be vey beneficial visually not just photographically. As to whether you need one is a personal preference depending on your tastes (which if like mine can vary night to night).
I gave no experience with the ES unit but have used the Paracorr with tunable top (model just before P2). I often observe with a 16” f4.5, 10.1” f6.4 and 6” f5.5 without the Paracorr in place simply because the coma doesn’t bother me. However when I do use a Paracorr, I can immediately see the difference even at f6.4. Note, I also have a Skywatcher 10” f4.7 but I cannot use a Paracorr with it because Skywatcher in their wisdom, (or lack thereof) put a stop inside the draw tube preventing full insertion of the Paracorr and thereby preventing me to reach focus with a Paracorr in place. The same stop also prevents my 2” Astro-systems Barlowed laser from fully inserting so I am unable to see the return beam spot? It is the black focuser not the white one.
Anyway back to whether you need a coma corrector and I say first get some quality eyepieces that are well corrected that will show you only primary mirror coma and then decide if that coma is bothersome. A coma corrector corrects primary mirror coma; it won’t do much for eyepiece aberrations.
The Tele Vue unit has a 1.15x amplifying factor and whilst some may say a unit with 1x factor is better, there is a reason for the 1.15x and that is to flatten the field ever so slightly. This is beneficial for some eyepieces such as the 22mm type 4 Nagler which in a TV-101 is pristine and fiat to the edge of field but in a typical Newtonian, say 1500 to 2000mm focal length, there is very slight field curvature visible with the 22mm which the Paracorr cleans up very nicely.
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