The partition coefficient of the ester in question is important because is effects how long the drug itself stays in the system. If the testosterone transfers too quickly from the oil to the blood, the result is a sudden spike in testosterone which then rapidly drops once the dose has been used up. In the example of free testosterone injected into the muscle from a water suspension (as in Aquiviron, mentioned above), the testosterone is essentially immediately available to the bloodstream due to its low partition coefficient, and thus there is an immediate spike of testosterone which is used up quickly in the body.
Side effects of testosterone enanthate include symptoms of masculinization like acne , increased hair growth , voice changes , and increased sexual desire .  The drug is a synthetic androgen and anabolic steroid and hence is an agonist of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT).   It has strong androgenic effects and moderate anabolic effects, which make it useful for producing masculinization and suitable for androgen replacement therapy .  Testosterone enanthate is a testosterone ester and a long-lasting prodrug of testosterone in the body.    Because of this, it is considered to be a natural and bioidentical form of testosterone. 
Water based or Aqueous testosterone suspension can peak in the blood stream within minutes of being injected and is metabolized very fast. Because Testosterone Suspension remains in the body for a short time, it has to be injected very frequently. In most cases Testosterone Suspension has to be administered daily or few times a day in order to maintain a stable blood testosterone level. If Testosterone Suspension is your preferred choice you can rotate injection spots each time rather than injecting the same location each day. This form of testosterone is not highly recommended and is often used by very experienced and extreme athletes, body builders and power-lifters. This testosterone form give the best strength results and a high aggressiveness. It also exist a testosterone with no ester and oil based called TNE (Testosterone No Ester).