Hi Norman,
Welcome to the Mattress Forum! 
I can’t speak to the pricing policies of different manufacturers, as I wouldn’t have access to their budgets and costs of doing business (raw materials, transportation, assembly, advertising, staffing, etc.). All I can speak to is the componentry.
The Sleep Essentials (you didn’t mention which model) uses 100% natural Dunlop latex supplied by Latexco under their Naturalux name. While Latexco has the ability to source it from any company that makes 100% natural latex, it would almost always be made by Latex Green. Sleep Essentials also makes their mattresses without any flame retardant barrier, so you need a doctor’s prescription for this (they can provide you with a sample form). They state their mattresses are made without any flame retardant chemicals (which is true), but mattresses don’t need to use chemicals to pass federal flammability regulations. Layers can be rearranged on their mattresses (they use a 6" core with 3" above that), but I’m not familiar with any return/exchange polices that Sleep Essentials may have in place – you’d want to contact them about that before placing an order.
Spindle uses 100% natural Dunlop latex using the continuous pour process from Mountain Top in Pennsylvania. They pass the federal flammability regulations using eco-wool, and their cover uses organic cotton. Spindle is well-known for providing affordable pricing on their mattresses, and does offer some very good values for 100% natural Dunlop nationally. Spindle uses three 3" layers of latex, and the layers can be rearranged and there is also a 365 day exchange policy (see here).
I do think highly of Neal at Spindle, and they are a member of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration.
Both of these mattresses use good quality and durable materials, so you’re choosing between “good” and “good”, but there definitely are some pricing and feature differences which you’d want to analyze as part of your personal value equation.
Phoenix