Nearly 40 - which hair loss brands work best, eclipse, regenlabs, PRPkits, DrPRP, emcyte etc.?

There really is no good clinical data with peer review, double blind randomized studies or meta analysis saying that one prp company is better than the other and they compared the different companies. I would choose a prp that uses at least a prp centrifuge device that is fda cleared. Results can vary about 1/3 get very good results another 1/3 get average results and about another 1/3 gets no results. Combination therapy yields better results with prp

Choosing a PRP system is a very important decision because there are so many different ones on the market and they are very different in terms of the type of PRP they are able to produce. Various research studies (Fadadu et al, 2019; Magalon et al 2020) have been published comparing different PRP systems and shown that less than half of commercial PRP systems are capable of producing PRP with a concentration of 1 million platelets per microliter, which is the minimum concentration needed to meet the definition of true PRP.
In general, PRP systems can be divided into single or double-spin systems. Single spin systems tend to produce PRP which is very pure (low red cell and white blood cell concentration), but low in platelet concentration; while double-spin systems are better at achieving high platelet concentration, but tend to have higher number of red cell and white cells in the final PRP.
The platelet concentration is most important as the platelets contain all the growth factors which are involved in improving hair growth. Besides concentration, you also want to have enough platelets delivered to the scalp during each treatment. For example, we might want 4-6 billion platelets per session, which would require 4-6 mL of PRP at a concentration of 1 million platelets/uL. On the other hand, if the PRP concentration was 79,000/uL (like some single-spin PRP kits have), even with 6mL, only 474,000 platelets would be delivered.
To be safe, make sure your provider is using a PRP kit approved by the FDA, Health Canada or your country's regulatory agency. Ask about concentration, purity, and total dose of platelets per session. Is the PRP tested before injection?
Also, I recommend a full medical history, appropriate blood tests, and even trichoscopy if possible to consider other causes of hair loss including nutritional deficiencies (e.g. iron), hormonal causes (e.g. hypothryoid), etc. PRP should be considered as part of a comprehensive approach to hair loss. There are also complimentary treatments which can and should be used alongside PRP to support hair health and growth.