I find the healer feat is bonkers good at low levels. What the healer feat lacks is high punch big numbers at high levels from spells like heal, and the once per target per short rest is a bit restrictive, but it's a ton of extra healing regardless.
The 1st level vhuman with the healer feat in a party of 4 heals an average of 102 hp given 2 short rests. It's an average of 8.5 for each of the 4 characters 3 times. The hit dice for the classic fighter, cleric, rogue, and wizard has 15 hp of magical healing if the cleric uses both 1st level slots on cure wounds. The typical hit dice healing would be about 28 hp because there's only 1 hit die each at that level for 43 hp healing. The healer feat is the difference of 43 hp of healing versus 145 hp of healing. The kit is well worth the cost for a few kits for every party member to carry one. The onus moves to the DM to limit supply.
Using the same party at 2nd level and the healer feat increases to 114 hp. Another spell slot IF uses for healing moves up to 27.5 hp. Hit dice healing doubles up to 56 hp for 83.5 hp of average healing without the feat versus 197.5 hp healing with the feat. The healer feat still more than double healing at 2nd level.
Looking at 3rd level and the healer feat increases to 126 hp. The cleric can cast prayer of healing up to 2 times and cure wounds up to 4 times at this point and between the two spells is looking at 130 hp of healing. That's the benefit of of an efficient healing spell. It's not likely a cleric will use every spell for the most efficient healing, of course, and this is for argument's sake for the moment. It takes every spell the cleric has at 3rd level to even begin to compete with the healer feat. The feat is literally like adding the healing of a 3rd level cleric to the party. Hit dice healing also increases to 84 hp. The difference with feat vs without the feat becomes 340 hp of healing vs 214 hp of healing and still a huge jump.
At 4th level the number of hit dice exceeds the number of times the healer feat is used based on the 2 rest assumption. The healer feat is 138 hp, hit dice healing is 112 hp, and the cleric may bring in up to 194 hp using every spell on healing with the assumption of a WIS increase.
If a person looks at the healer feat at 4th level it looks really really good. It's massively better than any other healing available at those early levels. Each short rest worth of healing only looking at the healer feat is 11.5 hp per person per use while prayer of healing is 13 (or 12 if a feat is taken) hp per person but takes spell slots instead of cheap components. Based on those assumptions given the healer feat at 4th level still exceeds hit dice healing and a cleric needs to go out of his or her way to compete. In a campaign where more short rests become available or more individuals might be healed (like a wilderness or city based adventure) the amount of healing can increase drastically.
Hit dice healing in the above party doesn't match the healer feat until 6th level, and it takes 7th level to really start to pull ahead. The cleric using multiple party wide or higher slotted healing spells per short rest has an advantage at similar levels and the heal spell for a fast bigger number. By 12th level spells can outshine the healer feat. The feat is doing 19.5 average hit points of healing for 234 hp and hit dice have pulled well ahead for 336 hp of healing. By that point hitting a PC once each per short rest for ~20 each is still very good but not so over powered barring extra short rests or more potential targets.
Even up to 20th level the healer feat is worth 27.5 hp of healing per target with a short rest recharge. Song of rest is 6.5 hp per target. In the party of 4 PC's that adds up to 330 hp of healing. A paladin's lay on hands is 100 hp of healing. Mass cure wounds in a 5th level slot is 18.5 hp of healing for 74 hp of healing in that example. Prayer of healing in a 5th level slot is 27.5 hp per target but it takes 10 minutes instead of 4 actions.
The healer feat outshines class abilities and is easily comparable to healing spells. Change that to a party of 6 that takes 3 short rests and the feat heals 660 hp at 20th level for 2.4 healing kits worth of charges. At 27.5 hp per .5 gp cost when all it takes is each person to carry their own kit the feat is solid at any level. It's even hard to lose hp healing to over-heal based on static increases with only a d6 die
Since you won't be using Healer every round, grab some vials of acid or alchemist's fire (or even oil, if you're strapped for cash) to use with Fast Hands when you happen to have a spare bonus action.
Or caltrops or ball bearing or etc; or pick some pockets with sleight of hand. Fast hands is good because fast hands is good, but it competes with other cunning actions. The healer feat isn't good because of fast hands. It's good because it significantly more healing than spell slots and hit dice combined in the first couple levels of the game, and a lot of healing regardless after that.
I ❤ fast hands. ;-)