NI-CDs are definitely worthwhile if you can get them for next to nothing and if they have life left in them. They are not economical to manufacture for consumer use anymore and some places like EU, possibly US as well ban use in consumer products and EVs because of lack of disposal and recycling options, for environmental reasons. If they are already available and you are giving them a new home, you're probably doing nothing wrong, I would just ensure you mount them on a sealed surface to avoid contamination if they do leak and work on them with the appropriate PPE. From what I hear they don't have as much risk of explosion and fire as lithium. They are still manufactured for emergency back-up and aviation use which does have exceptions in the laws where they are otherwise banned for unsustainability.
I have picked up around 30KWH of brand new emergency lighting NI-CDs from a lighting auction clearance here in Australia. I'm currently examining best charging methods and connecting them. It's a bit more complicated because they can't be paralleled when charging, and in order to fast charge them you can't rely on a particular voltage to determine full charge detection, you need to either use a thermistor on the cells, or a circuit that detects when voltage drops off again when fully charged. You can also trickle charge them over about 16 hours which may work best for solar power. A system may have to be split and switched to have one pack in use and one pack charging at any time. If there is the need to parallel them to provide more current, apparently complete series strings can be top end parralelled, by paralleling an entire series string, instead of paralleling every set in a series string like what is done with lithium ion. This is because they only charge with a voltage a bit higher than the voltage that each string would supply so not much chance of one complete series string draining into another. They do have to be separated from being in parrarel when charging so switching them apart with one relay per string to charge them would work like this. With the size of the cells in the picture, you would probably get away with sufficient size packs with one only in parallel so wouldn't have to worry about this.
I've heard mixed reports about whether or not the memory effect is actually an issue or not, but it was originally discovered in satalites that were being charged from solar power, and then discharge at the same rate with every orbit of the earth, so may be something to take into account with solar power.
From what I've read, they are a good robust battery with a similar lifespan to Lithium Ion, people just remember how much they failed in power tools because manufacturers didn't provide a decent charger and cordless drills etc. often used after a only a few hours of charging because needed straight away, when the simple plug pack trickle charger provided required 16 hours, an overnight charge to charge the battery fully. Things have changed now with Lithium, A BMS and a decent charger is required for safety reasons so manufacturers have been forced to incorporate a decent standard of quality into batteries and charging, so have incorporated accurate charge level displays and other features which have not cost a lot extra than this.
Fast changing of NI-CD batteries only became popular when NI-MH Came along in the 90s, since the overnight trickle charge method with no full charge detection that was widely accepted by Manufacturers using NI-CD cells until then damaged NI-MH cells. Apart from that, both types of cells charge mostly the same using the fast charge voltage drop detection method for full charge.
There are some reports that NI-MH cells might be making a comeback with some manufacturers, NI-MH along with NI-CD have been largely known to be superceded by lithium in recent years, but with current issues with cost and safety of lithium ion, as well as possible improvement in NI-MH cell technology since they were popular, and hopefully an improved cell lifespan over the 500 cycle that they were previously commonly rated at (about half of NI-CD lifespan), some manufacturers are reported to be giving them a second look and considering going back to them in some applications. It is highly unlikely that NI-CD will make a comeback though, with the exception of the limited applications that they currently are still used for because of sustainability and environmental reasons of limited disposal and recycling options and the increased cost of manufacture now.