"Hormone blockers have almost no side effects at all." Okay. Let's verify that by looking at Mayo Clinic's information page about puberty blockers (https://www.mayoclinic.org/diseases-conditions/gender-dysphoria/in-depth/pubertal-blockers/art-20459075). It states that the effects of blockers are reversible. That page references the World Professional Association for Transgender Health Standards of Care 8, which says the same thing, that puberty blockers are reversible. (https://wpath.org/publications/soc8/) It doesn't cite any studies to support that claim, but it does cite previous Standards of Care publications 6 and 7. (Version 6 was published in 2001, while Version 7 was published in 2012). Regarding Version 7, on page 13 of 67, it describes
"Fully reversible interventions. These involve the use of GnRH analogues to suppress estrogen or testosterone production and consequently delay the physical changes of puberty." (https://web.archive.org/web/20180327142657/https://www.wpath.org/media/cms/Documents/SOC%20v7/SOC%20V7_English.pdf)
That section cites a 2009 study (https://academic.oup.com/jcem/article/94/9/3132/2596324) which states that even "prolonged pubertal suppression" is reversible. That study has a section called evidence, which states "In addition, the hormonal changes are fully reversible, enabling full pubertal development in the biological gender if appropriate." That 2009 study cites a 2008 paper, stating "In our view, these early hormonal interventions should not be considered as sex reassignment per se. Their effects are reversible." (https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1743-6109.2008.00870.x)
Finally, that paper in turn cites a paper from 1998 (https://www.et-fine.com/10.1007/s007870050073), which is a single patient case study. That case regarded a female patient who later had a mastectomy (so the blockers didn't even work anyway?) and a hysterectomy. How the hell can that alone confirm that blockers are reversible for male patients, a completely different subject? Furthermore, the paper doesn't even mention that the effects are allegedly reversible.